Fresh Cab is one of the best biological rodent repellent on the market in 2014, according to EarthKind. It consists of a small packet soaked with several essential oils. The smell of these oils is supposedly offensive to rodents such as mice and rats.
Ultrasonic rodent repellent devices do not work very well, according to The San Francisco Chronicle. The rodents might be frightened of the noise at first, but they quickly get used to the sound and ignore it.
The most effective way to repel rodents is to remove all food sources and to block all possible entry points into a building with wire mesh. Rodents can chew through wood but not through wire mesh.