I use the PetSafe Radio Fence with the Small Dog Collar. It is great, because it is not too heavy or bulky for my small dog, and it has worked exceedingly well. The only problem is that the small dog collars eat batteries, like I eat ice cream. The collar will burn through a battery in as little as four weeks, and the replacement battery 'corks' from PetSafe are a whopping $8 each!! I figured out how to replace the battery inside the cork, for about $1.50. Here is the video of how to do it. I hope it can help some of you.