Liability Release for Tenant's dogs

We rented out our house that we own to a tenant. On his rental application he included 2 dogs that he described as a Mastiff mix and a Bullterrier mix, which we agreed to, according to his description of them. After he had moved in, we received note from the neighbors that these dogs both looked like pit bulls and also injured a neighbor's dog. He is reluctant to get rid of them as he claims we agreed to the dogs. He has also not provided proof that these dogs are not pit bulls as he claimed on his application and repeatedly thereafter.
At this point we feel the only choice we have is to let him keep the dogs on the premises. But we would like him to sign a release from liability in case the dogs cause harm or damages to persons/animals or our property. How do we phrase such a liability release? Can we be held responsible in any way for anything his dogs do?

That liability release is useless. It would not release you from any liability from anyone who was injured or had their pets injured by his dogs. You would still be sued! The tenant's own insurance policy to cover the pets would also not release you from liability. (And if your own insurance company found out about pit bulls on the property, they would cancel your insurance very quickly. That breed is on nearly every insurance companies liability list.) You will most certainly be held responsible for anything that tenant's pets do!

I suggest you send him notice of lease violation for failure to properly disclose the breed of dogs. Serve him with a Perform or Quit notice to get rid of the unauthorized dogs immediately (you didn't authorize pit bulls,now did you?) If he refuses, file to evict him based on his misrepresentation of the dogs. Take photos of the pets immediately, and post beware of dog signs. (That won't release you from liability, but it may keep some people away from the fence.)

In future, don't accept any pets based on the tenant's description. Meet the pet yourself, take photos, then decide if you will authorize it. And check with your insurance company about what breeds they will not cover.

a bullterrier IS a pitbull....

Send notice (Perform or Quit notice) that you will no longer allow the dogs since they have injured another dog and let him know that a police report is being filed. You cannot allow agggressive dogs on the premises as the insurance agency will not allow it. Give him a set number of days to remove the dogs. Then file to evict.