Creating unique url IDs for items (list/item)

Hi, I'm wondering what the best way to create a completely unique code for items (outside of blog posts and events) - or the best way to solve the problem below.

For example, I'd like to generate a URL like:

/thing.php?s=1234_item-name

Where the 1234 is a unique code and 'item name' is generated from the item's title.

The problem I run into is that there may be multiple items with the title 'item name'.

Many thanks for any help or tips.