You are welcome to take whatever approach you like. However, I'd like to make a point from the other side as it were. I work for a large company who for various reasons outsource much of their development and who tend not to get source code rights (stingyness being one of the reasons). Were I in the position to change this I would. As a businessperson I would never allow source code rights to a critical business system to belong to an outsider. Theres two reasons for this, the first is that it means I am funding the R&D for a product that I cannot prevent from being sold to my competitors. The second reason is that it could at some point prevent me from realizing my business goals. Since I wouldnt have the source code rights if I needed a change then I would be putting myself at the mercy of the third party vendor to provide that change but without any guarantees that the vendor will prioritize my requirements in the same way I would.

I've watched both of these issues play a critical role in my firms competitiveness. Changes that source code ownership would have made trivial have dragged on for months costing us market share and vast sums of management time to resolve. Likewise features developed just for us have appeared in the mainline rollout of the software which has been delivered directly to our competitors.

What does this have to do with you? Well nothing much, except that if I were the guy making the decisions and you said you would end up owning the code that I paid to have written you would be laughed out the door. I wouldn't want to do business with someone who so completely misunderstands the role that software plays in the modern businessplace and who obviously prioritizes their own benefit over the best interests of my business.

The bottom line is that its reputation you want to develop, not an inhouse store of code. Make a name for yourself as a good conscientious developer who does good work and holds the clients interests above all else and youll make a lot of money. Come across as a schemer who wants to get paid to make a cake and to keep it and you wont. At least in my opinion anyway.