First of all, this is absolutely impressive in concept.

Yes, it's too easy that way:

    map.pO = map.placeObject;
    map.placeObject = function(x, y, w){
        return map.pO(x, y, w=='block'?'empty':w);
    }

Does not even need call. But while you cannot protect from `Function['p'+'rototype']['c'+'all']`, I think using `defineProperty` to stop mucking with the code would go a long way into preventing blatant cheating at little cost. That or enclosed reference funcs.

Btw, you trust the level increment counter before succeeding in loading the level. Right now calls are 503ing, so basically I'm [gisting bogus solutions](https://gist.github.com/anonymous/f1b06d63848d6d013e26) but it's also saving those bogus level ups in localstorage...

Aww, I thought that was to easy. That trick works for basically any level.

Also, is there a good way to completly prevent tampering with functions, or is this just going to be an arms race?

I did a similar thing for level 6: http://pastebin.com/aScFtgK8