Coolant Leak

We have a 2002 Jeep Liberty with about 56,000 miles on it with 3.7L engine. For the last two years we have had an issue with a coolant leak that can not be found. The dealership has looked at the issue a couple of times and they have not been able to locate any leaks. However, the coolant is slowly disappearing and needs to be topped off. We have not noticed any smells, puddles, and the vehicle does not run hot. Any ideas would help.

Thanks.