How clear does a Possession Clause need to be in a home purchase agreement?

My wife and I are buying a home, and in the purchase agreement provided by the sellers, it reads "Possession: Possession of the Property is to be given with delivery of warranty deed and payment of Purchase Price". That is all it says on the matter. Do I need to add a stipulation that if they aren't out, that we will charge rent per day that they stay past the date of payment and deed transfer, or is the current wording enough to be able to seek those damages should they stay post the transfer date?