Anyone validating URLS passed to your app???

[eluser]mindprojects[/eluser]
Hi guys!
I was wondering if anyone has used before some kind of url validation in a web app,as such as appliying an md5 string to the url to validate the url itself avoiding a user to modify it hand by hand.

Suppose we are editing a post(id is 10) belonging to a user 'Pippo' passing the url:

http://myapp/post/edit/10;

I want to avoid that a user can modify this url appending the id of another user post.
Obviously i should che it in my edit function,if the user can edit this post,but,why not appending an md5 string to the url itself,where the md5 = md5(uri string + my secret)?

The result url would be:
http://myapp/post/edit/10/mdf3fef443fwerw....(32chars)

Is it a good idea?
Thanks guys,any suggestion?