there is no foolproof methods. If WC3 can open the map, cheaters and theives can. Best way to protect a map? Have an easy to remember download location and spread the map.
Use Vexorian's Optimizer. It's not failproof, but it sure helps since few who bother de-protecting know JASS. Plus, some options will crash the editor if someone tries to open it. Vex's Optimizer can be found on the site.
If you want me to protect things for you I will happily, if thats what your asking.
The mods can read PMs (teehee) as far as I know, so If i tried to steal it it would be neg rep and ban city for me.