Leaks can be attributed to several factors, so you'll need to determine the cause before remedying the problem. One of the most common culprits of leaks is a bad fit. Check that your dog's diaper provides full coverage and make sure the hems are snug enough to seal the openings without pinching. Inadequate absorbency can also lead to leaks. If you suspect this to be the case, consider switching to a diaper with a higher absorbency rate or increase your existing diaper's capacity by inserting a cloth diaper booster pad.