Regardless of anything else about those shock collar systems, remember this: an invisible fence keeps nothing at all OUT. So neighbors' dogs, strays, coyotes, etc., will be free to cross onto your property. If they're friendly and your dogs are fixed, no big deal, but if one unfriendly dog should happen onto their territory, you've got a dog fight to break up.

Another thing is that they're proximity based. So when your dog does decide it's worth the pain to chase the deer that just crossed its boundaries, it's going to get a shock every time it tries to go back home.

An above ground electric fence with a solar charger shouldn't be prohibitively expensive.