Do you give a expiration date on reprint licensing?

That would seem to be almost impossible to enforce. I assume you're talking about usage permission for digital files that you provide to a client. You can charge based on the type of use that's allowed, and for something like advertising it wouldn't be unusual to have a specified time period, but for reprints of event photos...?
It is possible to provide the image files on an encrypted disk that has an expiration date, but I don't know how effective that would be. Files could always be copied to another medium.

Thank you for your time and answer...

Even if not enforcable, it is a good idea. The legitimate businesses will abide by it.

I include it in my contracts. There is a time limit on reprints and commerical use, but there is often an exclustion. If an image is used, say on a website, it can continue to be used indefinitely. If they stop using it, and want to start again beyond the time limit, that requires another license.

^^Thanks Nathan, what kind of time limit would be good? 1yr, 5yr or more?^^

I do not do that. With my commercial clients--always business portraits and the like--the images have a natural "expiration" anyway. They will always have to update them in a year or two--with me if I've done the job and my marketing properly--so I toss them the bone of "perpetual" use, even though I know it's really not worth much to them.