Data locking in a web application

An anonymous reader writes: We have recently developed a multi user application and deployed it to our users. This is a web based application that used to be a windows application which was written in Delphi using Paradox databases for the client database. In the windows application we used the ability in paradox to lock records which would prevent users from editing the same data. However, in the web application we did not add in a locking facility for the data due to its disconnected nature (at least that's how I was shot down). Now our users are asking to have the locking back as they are stepping over each other from time to time.

I have been assigned to look at best practices for web application locking of data, and figured I would post the question here to see what others have done or to get some pointers to locations for best practices on doing locking with in a web application. I have an idea of how to do this, but don't want to taint the responses so I'll leave it off for the time being.