To prevent painful tears and other problems, trim his nails once or twice a month if your dog doesn’t wear them down naturally. If you can hear them clicking on the floor, they’re too long. Dog toenails have blood vessels in them, and if you cut too far you can cause bleeding — and your dog may not cooperate the next time he sees the nail clippers come out. So, if you’re not experienced at trimming dog nails, ask a vet or groomer for pointers.