Since you dont say exactly what kinds of damage your yard/garden is suffering because of the animals, I can only give you some general pointers. I always tell people that there are regional and species differences that can affect the solution too, so if I were you, I would also talk to the people at the local extension office.
Are you feeding birds? If so, only use a feeder that the squirrels cannot get access to. As long as there is a ready food source for the squirrels, theyll be more than pleased to stick around. I know that Messina makes a squirrel repellent, but I havent tried it (I do like their rabbit repellent): http://messinawildlife.com/. In fact, they have a gopher repellent too.
People call several small animals gophers, and they might be referring to ground squirrels or chipmunks. First, be sure you know what animal youre really dealing with (again, extension can help). If they are true gophersprobably pocket gophersthey will be difficult to get rid of. You can try trapping them with a special gopher traptry a farm supply or hardware store for that. Or you can try flooding out their tunnels with a garden hoseyoull probably have to do that repeatedly. Or you can fence the yard or garden area, and bury hardware cloth 2 feet into the ground. Or you can hire an animal control professional. Not sounding too positive, am I? Sorry about that, but those gophers are stinkers. If you do manage to get rid of them, keep a watchful eyetheyll probably try to move in again.