We made this mistake. I thought I knew collies because of growing up around them, but I had missed a couple of essential elements.
1. They love to run free
2. They love the company of other dogs more than humans or cats (males even more so)
Having a decent 'in town' yard, 3 family members, plus a kitty I thought we were all covered. It turns out he wanted even more space and, the bigger issue, he craved the company of other dogs. We were unable to get a second dog and in the end we called collie rescue to help us re-place him. When we did we were very specific about his behaviors and needs to help ensure that another family did not make the same mistake. It is terrible seeing your child cry and not being able to resolve it in a happier way. Not to mention missing the crazy mutt. (technically he is a champion pure breed, but we were not that interested in that part, I just feel it would be wrong to 'muddy' his reputation.) P.S., we didn't buy our dog, he was being 'retired' and looking for a family.