The fact that he is not on the lease really won't help. Sure, it might make it easier to have him evicted, but, you might have to have your landlord evict him as you may not be permitted to. Plus, if your lease does not permit long term guests, you may find yourself in violation of the lease for allowing your son to stay.
Now, if your son sleeps on a couch and contributes nothing to the household, he could be considered a lodger and is subject to being booted out the door If, however, he has a room and/or contributes rent or in other significant way to the home, you may well find yourself having to treat him as a tenant.
The ONLY WAY to control his guests is to NOT allow him to live with you. As long as he resides there, he can have guests over and the police will do nothing at all to boot his guest.
So, if you want your son to live with you, you will have to deal with his friends.

