I didn't take time to read all the replys to this, so I might be repeating some things that have been said already.
Making a long story short, the answer to your question is that you can't. Even VFP apps that are 'branded' with REFOX can be decompiled. I acutally purchased a copy of REFOX at one time, and after playing around with a HEX Editor for a while I found a way to even decompile that. It did take me a fair amount of time to figure out how to do it, but repeating the process only takes me like 3 minutes. I even sent the info to REFOX (becuase I kinda want my MONEY back seeing how it doesn't do what they say).... so far they've never responded.
Anyway, best thing you can do is to try to brand it with REFOX, but keep in mind that it's still possible to decompile if someone is willing to spend the time (like I did) to figure it out.

>It is now a known fact that our FoxPro/VFP source code can be obtained by third party decompilation tools like REFOX. Please tell me how can I protect my software and source code so that my software doesnot get decompiled. Are there techniques or tools for this?