Rats do make fantastic pets, domestic bred ones though lol :)
I would leave him if he isn't causing any harm though I am soft like that.
I was clearing my garden out with a friend a few weeks ago and we found a dead one in the garden, potentially cat related! They had something outside the other night too which I initially thought was a large mouse but have a feeling it might have been a small rat.
I get the even more personal treatment boxtops, have woken up twice now to find two very smug cats sitting on me with dead bird of the moment sitting in my lap!