The constraint that I have right now is that a program (e.g.,executable) needs to leave my hands...

... then there is no reliable technical solution. Obfuscation only keeps out the least determined. Anyone sufficiently determined such that contractual means (or even common courtesy) are insufficient to work with you appropriately will find obfuscation trivial to overcome.

Your best option is to work only with people you find trustworthy.

Your second best option is not to distribute software to anyone.