- Retain a lawyer in the developer's county
- Have them formally assign any and all copyright for the developed software to you for the value received (payment and other consideration) have the lawyer do this
- Have the lawyer you retain copyright your developed software IN THE DEVELOPER'S country.
The developer, however reputable he may be, will know you are using legal council in HIS country and would have easy access to his country's courts.
Now is it worth these added expenses? Your call ...
If it's possible -- get a patent.