Carpenter ants in my back yard?

I have a Trex deck along with a wood fence in my back yard. The Trex deck is close enough to the ground that there is no way to get underneath it. The last few weeks I have been seeing black ants (larger than sugar ants) crawling along the fence and sometimes on the deck. I am assuming they are carpenter ants? I cant see any type of ant hill or nest that they are going to. (There is a large, open field on the other side of the fence. ) I am worried they are eating the fence or the decking supports, and that they will make their way to my house. Since I cant see where they are coming from or going to, I have no idea what I can do to get rid of them. Any suggestions would be helpful. (Also, I own a dog so any poison ideas have to be safe for pets)