If a student ever challenges you with criticisms of the reliability or validity of geological age-dating methods, point out that...

1. all such critiques so far have been soundly discredited, and
2. there is, to date, NO empirical evidence or study that even suggests a young Earth (6.000 to 10,000 year age).

Provide a copy of Evidence for Ancient Earth (links and introductions for two articles, one by Christian physicist Roger Wiens, the other by radiochronologist G. Brent Dalrymple). Then tactfully and gently challenge that person to bring you a link to any empirical study pointing to a young Earth. After all, this is the way scientists test alternative ideas.

Furthermore, seriously consider providing a few experiences for your students that offer compelling evidence for a very old Earth (several billions of years). Take a look especially at these on the ENSI site:
Varve Dating (students actually count the annual layers in a sample of ancient lake bed sediments of the Green River formation, and extrapolate to several million years, based on the total thickness of the formation.)
Deep Time (introduces the Virtual Age Dating tutorial)
Virtual Age Dating (online tutorials; can be done as homework assignment)
Find these lessons (and others) in Geo-Paleo section of the Evolution Index