No problem. I would say that if the application is being used internally by the customer (i.e. an accounting program or intranet site) you are going to have an

No problem. I would say that if the application is being used internally by the customer (i.e. an accounting program or intranet site) you are going to have an easier time. If the application is a product/service they are selling to their customer, is a source of revenue, or is the marketing tool (i.e. their website) you are going to fight an uphill battle to convince them to let you keep the IP. Regardless, I would be clear from the get go and if you are looking to retain ownership I would make sure it is spelled out clearly who owns what. You may even consider a nuclear type option where they have a buyout right down the road if you do retain ownership. Either way, I would consult an attorney before signing anything.