Well, we have a Laburnum Tree that the snails love to cluster onto! We have to de-snail the tree trunk every so often, or the snails make their way down to the baskets.
When we moved in the house was empty for a year before, and the tree was covered like a boat with barnacles!!
We took buckets and buckets off and believe it or not took them for a ride in the car to some waste ground to get rid of them, cos we thought if we dumped them near by they would all crawl back!!
So we were told anyway. Unless someone was playing a joke on us 
I just couldn't face trying to kill that many of them Yuck!!