You could add a license term similar to the term from the Affero GPL v3 mentioned herehere:
if you run the program on a server and let other users communicate with it there, your server must also allow them to download the source code corresponding to the program that it's running
You could also consider to put your programs fully under Affero GPL v3, or offer dual licensing.
If a competitor will follow your license terms is a completely different question, especially when he is located in a country with a different jurisdiction than yours. If you want to prevent yourself against such folks, you need to keep your source code in private.
 
                