An owl box would help with your gopher problem. They use them here to watch over the vineyards. Every vineyard around here has them. I can't remember which organization puts them up for free but they are an easy install as well. Your property looks perfect for one.
http://www.hungryowl.org/nesting_boxes/barnowl_where.html
An owl will likely fuck his dog up though. Little fella is lunch to a hawk for sure.
Snakes seem to be the easiest, but maybe tough to adopt? Idk, I'm not a snake guy.
As far as cats go, I think of it the same way I think of hunting and zoos. Sure we can keep animals alive longer in captivity, but you ever see a happy monkey in a zoo? My man Harambe pretty much committed suicide by zookeeper. Animals wanna be free to do animal shit. Cats fucking LOVE to hunt. They're natural predators. Adopt a group of cats and let em live off your porch. They might die after a few years, but they had a fucking blast hunting shit the whole time. Def way happier than fatass Ms. Puss-Puss who lives to be 19 hauling her fat ass from the couch to the food bowl. I think the cats will actually appreciate the security blanket (food/shelter when they need it) and opportunity to do their thing in a populated hunting ground.
The longer you have 'em around, they'll teach new cats you bring in everything they know about hunting. Pretty soon you'll have a lethal gopher-killing squad of badass ninja kitties. Real shit.