We have a brand new border collie pup (just 7 weeks old). She is so smart, very few accidents in the house, sleeps through the night in her crate, etc. The problem is.....she is bred to herd sheep and her instinct is very strong that she wants to chase our feet! She loves to tug on our pantlegs and bark at our toes. She's adorable now, but it won't be so cute when she's 30 or 40 pounds! Any suggestions?