There are a few things you can do to keep these little critters out of your yard, and I'm betting you have tried some of them already ... 1. Rodents take over in places where there is food, water, shelter, and/or mates. Since your yard is landscaped, I'm guessing that you may have drippers for your plants, nice shady spots where they can relax, and maybe even some snacks for them (insects or seeds, depending on which rodents you have). So the first thing you can do is to block any and all entrances to your yard with above AND below ground fencing. Once the fence is in the ground, you can work on eliminating the animals that are inside. 2. If you are not able to set up an exclusionary fence, then you could try deterrents. One of the best ways to deter animals is to give them a food source that's going to make them sick. If you give them something that will kill them, then their friends will move in. If you give them something that will make them sick, they will leave and tell their friends not to visit (usually). Normally, deterrents that work against other senses by using sound machines or visual cues don't work for very long. 3. Another tactic is to use natural predators. You mentioned that there are no snakes or coyotes out doing their jobs nearby so that means you will need to bring some predators in. One of the absolute most effective ways to keep rodents away is to encourage a predatory bird to set up shop in your yard or very nearby. Barn owls, for example, specialize in eating rodents, and will eat hundreds of them in a month. That number rises exponentially if you get a whole family of them to settle down in your area. There are a lot of resources available on the internet describing how to attract barn owls to your location. Another option is you could take in a couple of feral cats from your local humane society - since they are unadoptable, their only way out of the shelter is to be a barn cat/rodent hunter or euthanasia. This way you could save a couple of cats and your yard at the same time. 4. Some people have tried using mountain lion urine to deter rodents. It works, but you need to apply it often so this wouldn't be my first choice, and I definitely wouldn't use it as a single deterrent on its own. However, it's a good extra step you can take along with some other measures to complement your efforts. 5. The final option that I have for you is lethal trapping. You mentioned that you haven't had much luck with snap traps, but I encourage you to keep at it, especially if you have implemented an exclusionary device like a fence. Another lethal option is something like the Gopher X Pest Control System. It's pricey but I know someone who used it and he swears by it. The key is to plug up all the holes before you release the carbon monoxide. If done properly, it shouldn't hurt your plants and you won't have to dispose of the animals.