Casdon
At this time of year I use soda crystals, which clean the patio slabs and kill the weeds in one go. You do have to move the pots first, but if you sprinkle them on you don’t have to do anything else, the rain washes off the dirt and the diluted crystals kill the weeds.
Caustic soda crystals will probably clean the slabs and kill the weeds but pets feet will be badly damaged, glyphosate is going to be easily the cheapest way, it’s been used for 50yrs and has never been proved to harm anything, salt or vinegar are going to be much more expensive and less effective (I’ve tried them).
My current plague is moss on the gravel drive I’m going to try roof moss killer.