How to limit users to one comment per post

I am using WordPress as a petition site and hacking the comments system to work as the petition signup. I would like to find out how I can limit a user to post only one comment per post. So far I can limit each user to one comment on the whole WordPress site as shown in the code below, but that’s not what I am looking to accomplish.

Allowing users to edit only their page and nobody else’s

We currently have about 50 pages, each of which I want a user (eg, bob, rob, smith) to be able to edit only 1 page. For example, bob & smith each have their own page. I do not want bob to be able to edit smith’s page. I want bob to ONLY be able to edit bob’s page. I don’t care if he can see other pages.
Looking through the user roles, I don’t see a way to currently to do this- I only see how to allow restrict access on a global scale.