It's not so much an answer to the question of licensing, but if you're concerned about your potential customers decompiling your assemblies then you should look into Obfuscation.
Obfuscation is performed on your release builds and it heavily modifies the naming of classes, methods, and fields within your application. If a user tries to regenerate the source code using a tool such as Reflector they will be met with a high level of difficulty in trying to make the code compile or function.
Update: To answer Cyclone's comment: Dotfuscator is probably the best known since it's been shipping with Visual Studio since 2003 (I think; not sure if it's limited to specific VS editions). Some quick Google searches turned up a tutorial on using it in Visual Studio 2008, and also some alternative options.
