Does the landlord reserve the right to retain a tenants security deposit, if he doesn't give 2 months advance notice of moving ?

I don't think it is enforcible. Security is to protect the landlord from damages.

Dear Yonkers Landlord: A landlord cannot enforce any tenant obligation that is not contained in the lease, claim any penalty from the tenant that is not stated within the lease, or do anything with the security deposit that is counter to the terms of the lease. A landlord cannot enforce a verbal agreement that is not contained in the lease. If you were letting your tenant leave before the end of the lease term, make a written agreement to tie up the loose ends of the tenancy. If the lease has a number of months to run, and the tenant wants a release, you may bargain for a payment from the tenant to end the lease early and release the tenant from the lease.

No, security is to compensate the landlord for any damages done to the apartment during your tenancy or moving out. Once you have vacated you are entitled to a return of your deposit. If the landlord wants to retain any of the security he must give an itemized statement of the damages and the cost of repair. You can bring suit in small claims court for return of your security.