my tennants stayed 4 days past the end of the lease.....can I deduct that from the security payment

Did you discuss this with them?  ask them to leave?  was there some agreement, even an implied agreement, that they would be able to stay?  did their staying affect you in any way?  Was another tenant unable to occupy the property?  you should decide how much trouble was caused by them staying, and weigh the possibility of them claiming you improperly took a portion of the security.