Havent heard anything good about them i am afraid. urban foxes in particular get used to sounds. the only way to keep your girls safe is inside a 6ft plus high fence that has bricks around it so he who cannot be named cant dig in. we use all sorts of things to do deter him including male wee around the perimeter, sometimes a talk radio station on, varying the times we let them out and feed them and put them away. electric fence worked for a while til he got wise to it but really it is a constant battle.