Your fear is not unfounded. I am very familiar with the legal/court system in a south american country and I can pretty much assure you that any attempts to sue / enforce the terms of your contract to someone who is willing to break the law would be expensive and futile. That said, I personally know many top notch developers working remotely for US companies that would never dare to put their reletionships/reputation at risk by being careless/malicious with code. It is just to good a gig to risk.

* I guess if your code was sooo valuable someone could be tempted into cheating it could happen.. but if that is the case, a US developer would behave no different.