Annual Rent increase language in residential lease agreement?

[Anne-Britt Ostlund]

Hi All - I have two single family rentals right now and multi-year tenants.  We do a rental agreement every year, but of course I'm a softy and have a hard time raising rents.  Does anyone have an example of rental increase language that they put in their lease agreements?  IE./ '$X/month with the option to renew on Y date for +% prime ...' or something?  Do people do that?