Pets in a No Pet Lease

[Mike Savage]

Goodevening from NJ, 

I have a tenant in my 3 family Investment property/house that just got a dog without informing or asking me and has a no pet allowed written clearly in the lease. I came to know of it when my next door neighbor told me about it since I do not live there anymore. 

This tenant has been there for a little more than 2 years and has been a constant problem. He is on a month to month lease now since I did not renew the yearly lease. There are more people living in the apt than mentioned on the lease. He has tried to install cameras on his own in the front of house recently without my permission. He has also tried to escort money from me in the recent past citing some issues in the apt. etc. My Relationship with this tenant isn't good either.   

I do have allowed another tenant to have dogs in another apartment in the same house and has it written in his lease already. 

How can I deal with this situation, I do not mind loosing this tenant?  

How can I prove that he has a dog before taking any action? 

Thanks.. Mike.