There are many people that sell these things that will tell you they are very effective but every test I have seen done by the Ag research people at our state universities indicates they are a waste ot your money.
The best way to keep unwanted critters out of the garden is a good, tight fence (and an electric fence definately can help as well) that has part of the fence buried about 1 foot deep with a 1 foot section extended outward to discourage the burrowers.