I've done a fair bit of research into copyright laws (well in Australia anyway) - turns out if you design a house for a site the client has the right to build that house however only on the subject site! AND the big AND - it doesn't matter if you got paid or NOT!
The only way to avoid the issue is to ensure the client signs a contract that states they only have right of use IF they pay!
This means that if you indeed supply a design amongst hundreds of other designers - win or not they can still build your design on the subject land!
I had a funny run in on the very issue of copyright and my ownership of a copyrighted design. I was lodging an application for a design at the local council, when another designer walked came to the same counter to lodge a design. I couldn't help checking out his plans as he was standing right next to me. Blow me down though it was an exact copy of one of my own previous designs for a set of units.
I waited till the application went on public exhibition to get the details of the developer and then approached them direct to raise my issue! We then met to compare plans and walked away with a $10,000 cheque!