Make pagetitle solely alphanumeric

Hey all - was curious if anyone had thought about this. I'm having a small issue with users on one of my sites including all sorts of special characters in their resource "Title" field. This is interfering with my install of Disqus, as it pulls some of its info from the same field and special characters screw it up.

I would like to limit this field to alphanumeric characters and basic url friendly punctuation (pretty much dashes only - no periods or commas) only. Since it's a default modx field and not a TV, I'm not sure if this is possible. Anyone have a clue how to accomplish this?

Hi
You can write a plugin as in the rtfm example http://rtfm.modx.com/display/revolution20/Plugins (Plugins example Custom Validation)
Cheers