I have ASP.net application that is basically a data entry screen for a physical inspection process. The users want to be able to have multiple browser windows open and enter data from multiple inspections concurrently. At first I was using cookie based sessions, and obviously this blew up.

I switched to using cookie-less sessions, which stores the session in the URL and in testing this seemed to resolve the problem. Each browser window/tab had a different session ID, and data entered in one did not clobber data entered in the other.

However my users are more efficient at breaking things than I expected and it seems that they're still managing to get the same session between browsers sometimes. I think that they're copying/pasting the address from one tab to the other in order to open the application, but I haven't been able to verify this yet (they're at another location so I can't easily ask them).

Other than telling them don't copy and paste, or convince them to only enter one at a time, how can I prevent this situation from occurring?