Unexpected aggressive behaviour

It could be territorial, but at your dog's age, it is also possible that there could be a medical reason behind it. Could you try letting the two dogs meet on neutral ground and see how they get along then? If your dog is still acting aggressively towards the Lab, it might be worthwhile getting him checked over by your vet to rule out any medical issues.

Nothing to add to Blondiescot's excellent advice. Good luck.

Were they initially introduced on in your house? We had the same with my son's visiting dog and our new rescue when they first met in our garden (didn't want to take the rescue out at that time - it was fairly disastrous as rescue took great exception to the intruder!) The next few meetings took place on walks and nowhere near the house and these were ok. Then we met outside the house for a walk and brought both dogs in. We had removed all food/water and toys. From then on our rescue tolerated son's dog. They are definitely not best mates, but now get along ok. Take it slowly and initially away from the house.

Is the Lab entire? He is young and you don’t know what messages he is sending out to our older dog.
His “macho” male hormones may be triggering this response in your spaniel.
Try arranging for them to meet on neutral territory- park, open countryside or wherever is convenient.

Thanks for your comments. Both are uncastrated which might be causing the problem. Our mut has been regularly to the vets and is pretty fit. We made the mistake in first introducing them in my son’s home so this time met on common ground in the park. No luck, they instantly began trying to dominate each other and then in our house a couple of times began fighting. It is most distressing and a problem we have to solve.if we want to be able to get together as a family. My other son’s dog and ours get on very well and they always have him when we go on holiday.

Dogs are like people, they don’t all like each other. I think your dog feels threatened by having a younger, bigger dog in his home, so he’s guarding his territory. Is your other son’s dog smaller and/or castrated, because if so he will be seen as less of a threat?
Good luck with getting to the bottom of this issue.

Always always introduce dogs on neutral territory. Lift any toys. Do not give treats. Dont make a fuss of one dog. The older dog may feel threatened by the young dog. Too much testosterone in the air. If incomer is staying at feeding time feed in separate rooms or feed one outside.

We have a border terrier, DD has a Viz, both neutered males. Viz has been a regular visitor since he was a few weeks old, BT is a year younger and has known Viz all his life but basically is just not happy when the viz comes to stay. Not aggressive but constantly "on guard" It is such a shame, they both compete for attention and although it is manageable it is not a relaxing situation. I think Casdons comment is at the heart of the problem

Casdon has expressed my thoughts well
You have two entire males, one ageing, one going into adolescence so the older dog may feel the need to assert himself. The younger is likely tonbe in full teenage reactive impulsive mode
Vet check for yours.
Don’t let them mix, if you walk together, keep on lead. How much do yiu know about the rescues history

My 4 year old Springer guards me which is not good. He doesn’t like dogs running up to me. We’re doing our best to train it out of him with positive reinforcement for good behaviour but if we can’t nail it we’ll get a behaviourist. His started when a GSD ran full pelt into him. He’s certainly better with neutered dogs though. I must say I’m shocked that a rescue has rehomed an unneutered dog. That’s usually a given. It might be worth asking why they didn’t do it. Hope you get to the bottom of the problem soon.

I wouldn’t want my dog upset, he obviously feels threatened. Your son has the problem he needs to socialise his dog and get it neutered if it hasn’t been.

Your ten year old dog sees his home invaded by a young dog, twice his size, which to make matters worse is apparently the pet of a woman (your DIL) of whom your dog is fond.

Your dog is jealous pure and simple.

The young dog needs to be stopped from being agressive towards your dog - it is his home after all, and indeed from agressive behaviour towards any other animal, altlhough judging from your post there has not been aggressive behaviour towards any others.

I doubt neutering a young dog would solve the problem.

I would try not having the youngster inside your home for quite a while, but meeting up outdoors for walks with both dogs on their leads. And if possible your son or DIL should find out more about their dog's previous home or homes.

Have you ever had other dogs to your house before? If not, I would definitely say it is a territorial thing - if ever we introduce a new dog, even for a visit, we always meet them outside the house - EXCEPT when my daughter got a new pup. She came from a breeder in Wales - not a puppy farm I hasten to add, and was the sweetest little Basset pup .... both my daughters went to collect her, and having driven 4 hrs there and 4 hours back, they STUPIDLY just brought her straight in, and I didn't think anything of it, as I was with the DGD;s and was exhausted as well!

Then began the fun and games - my Golden Retriever HATED her! He was very aggressive towards her, would resource guard us, any toys or food - she was only tiny, and he is big for a Retriever ... he would literally stand over her snarling, and it was horrible! We had a behaviourist, valium, and eventually a full body work over, and as a result, his insurance has rocketed! Not a thing wrong with him whatsoever, he was just jealous! They now live apart as DD & family have since moved out for other reasons and I do doggy daycare for Meredith Basset, (she howls when on her own having been brought up with my 2!) and now they love each other, play nicely etc although I do have to pick up his toys as we will get the side-eye if she goes near something he thinks is his ..... It was entirely our own fault!

Sensible advice on here!

And grandTante, well said. He has been Top Dog for years and along comes a usurper, full of himself and DIL's new favourite.

He's jealous and defending his territory.

We had our small male adopted dog neutered but it didn't stop him hating other male dogs. He always loved the females, however, even in old age.

Try some parallel walking with them both, gradually get them so that the distance between them on the parallel walk is decreased.

It will help if the youngster is tired/settled before you do this. Be calm and confident, head up. Lead loose, and don’t try to focus too much on the dog. I’ve done this with one dog on the path on one side of the road, and the other on the opposite path.

When they can ignore each other just decrease the distance they are apart.

When this is going well walk with confidence through your home town go to an cafe with outdoor tables. Sit a few tables apart, chat happily to your son. Settle the dogs into a sit or down , then small fuss and treat (I’ve given a pigs ear that they’ve had under the cafe table). That’s a very high value treat, well with mine it is, also it gives them something positive to do while ignoring the other dog and you have a coffee or whatever.

Be confident and persevere. Remember everything you feel goes down that lead, and if you expect trouble you will most likely get it.

Good luck, and sorry for such a long post!

Thanks for a lot if very useful advice. They live a four hour drive away so we do not do day trips to see each other, meaning only meeting outside for walks would be difficult. I think you may be right in suggesting ours is jealous. Our son’s dog is not the instigator, he would I think like to play but ours is just determined to be top dog. I just hope constant vigilance and time will improve the situation. We have always had dogs and never had a problem before. Out dog is also adopted, we have had him four years and knew the previous owner, an experienced dog handler who trained him to a high level. He is usually the perfect dog, well behaved and affectionate so a big shock to see such aggression from him.