Ultrasonic repellers aren't quite as effective as the hype. Still think there some potential, after building quite a few. My problem was cats, had a neighbor with 23 regulars, and pretty much fed any animal that came around (eventual rat problem). Some of the cats found a new toilet, some got use to the sound, and mostly were cautious. Two of them weren't bother at all. It's just noise, that we can't hear, but there is always noise associated with the human population, whether we hear it or no.
Rats and mice won't nest, without a nearby source of food and water, need to try and remove access to any easy source. Would set traps, and keep an eye on them. Would stay away from poisons, a sick rodent finds a safe place to hide, which is hard to find and access. Smelling dead mouse in the house isn't good. I got two electronic rat traps, and they worked great, they never get a chance to take the bait. You pick up the whole trap and dump the corpse in the trash, reset and it ready for the next. Batteries last a good time, even with a lot of rats. Pretty sure there is a mouse version. Got them at Home Depot.
From work, they require 2 feet of bare ground around the entire warehouse, apparently rodents don't like to cross open ground.
