- "cementery" is just a little joke, self-explanatory in an appropriate context;
- "cemetery" and "cemetary" is YOUR "toy", YOUR rules, and is not obvious to an inadvertant reader, other than striking him as "mistake" at first glance. So, if you want to make a point, a statement, with the deviating spelling, you need to explain - and in that sense, I think it's second best option.
I agree fully, that's why I sort of pounced on your "cementery" to grab it <img src="/ubbthreads/images/graemlins/up.gif" alt="" /> - it should be self-explanatory. Thank you. And now I don't even mind the "ery". It suits cement better.