Prevent creation of overlapping dates

Hi all,

Apologies if this is already explained somewhere, but my searching didn't reveal anything.

I'd like to be able to set up the date field so that users cannot create repetitions whereby the duration if the event is longer than the repeat interval. (i.e., to prevent one instance of an event overlapping with another instance of the same event).

The problem is that many users seem to confuse the "end date" with the "repeat until date". And end up putting the end time of the *last* event into the end date, rather than the end time of the first event.

e.g., if someone wants to create an hour long event that repeats daily for this month, they often set start to 2012/09/01 18:00 (good), the end time to 2012/09/30 19:00 (oops!), and repeat until 2012/09/30 19:00 (good). The problem then is that every day a new event starts, but the previous hasn't finished. And so if you look at a calendar view for 2012/09/30 then you'll see 30 instances of the event.

If anyone has any clever idea of how to get around this I'd be really pleased to hear it! I think some sort of validation rule to check that instances of the event don't overlap would do it?

Thanks

Joe