Do you have own short (not necessary) domain which you want to use for some web presentation and as own url shortener? This easy plugin to MODx should help you.
This is an easy plugin that takes any URL and provide shortened version. Shortening is made from ID, so at the beginning you will have only one or two chars hashes - thats pretty short.
To every link is stored clicks count, so you will have an overview about how many people clicked on shortened version.