Most invisible fences have warnings on them that they are not for animals under a certain weight. may i suggest that you save up for a regular fence OR do what we do...... i have 4 Xpens that I hook together off the back of our patio..... it works perfectly!!!! (we also have 2 xpens that we take with us when we camp)..... the dogs have plenty of room to run, and yet I can keep an good eye on them. It would be difficult to keep track of them with the whole yard fenced in anyway!
