Carpenter ants are controlled by baits and sprays that you can apply. The fact they were treated two years ago does not ensure they won't return. The ants live in forests and wood piles and send out colonies every spring. You may see only one or two an evening, but even this small amount means you have a nest or scent trail which needs attention. Caulking is not an effective way to kill or deter these pests.
Read the articles at www.bugspray.com. They offer preventive and agressive treatment chemicals and baits. I'm sure you can find a solution that will allow you to deal with this problem.