wow.. sounds like dejavu.
My parents beagle was very stubborn. They live on 3 acres near a HWY. They tried a pin, didn't work. We didn't want to tie him cause keep in mind dogs are pack animals who want to be near their "pack" (that you LOL) So as a last resort we got an invisible fence. WORKED LIKE A CHARM !!!!!! I would recommend it. It kept him from being killed on the HWY , getting stolen, etc. He was a much happier dog too. He knew his boundaries and his territory and he learned it very quickly.
Warning, it is a PITA to bury the wire, etc. but definitely not impossible ! Also,, if you get one remember to keep the batteries updated.
We never had a problem with other animals coming around and attacking him . As long as you are semi aware of what is going on in the yard he'll be fine !!!!!!!
People tried to tell us it was cruel to zap him, etc . but let me tell ya, it's much worse to have a dead dog on the road !
GOOD LUCK !