Our security deposit is $100 more than one months rent to cover any unpaid w&s bills. If would be nice to have a security amount field next to the ren?

Our security deposit is $100 more than one months rent to cover any unpaid w&s bills. If would be nice to have a security amount field next to the rent amount on the listing page that we could enter an amount. Right now we are limited to items in a drop down list. i.e. One months rent, two months etc