Just an FYI......I had a very similar problem about 7 years ago. Neighbor lady(cat lover) started feeding all the strays that came around. Next thing you know, we, as in The Wife and myself, have a feral cat over-population problem. We have our back yard fenced in to protect our dogs, but it did NOT stop the cats from coming into the back yard, and pizzing all over and under our deck during the night when our dogs are inside.. I tried the boundary stuff and all it did was make my dogs not want to be around the deck, and no amount of spray would get rid of the cat urine smell
My final and permanent solution was to use a have-a-heart trap, and take the days catch behind my fence and give whatever it was a .22 caliber headache. Between the trapping, the red tails got a few and any stragglers ended up being road kill. Problem solved.