How do keep tree roots out of my compost pile?

My compost pile is in my veggie garden. Do any of you have problems with tree roots getting into the compost pile? It sure makes it difficult to get at the compost and using it.

How do you keep tree roots out? Cutting down so many trees is not do-able.

Moderator's note: added a more descriptive title to topic

 

Well I have an old shed door underneath my pile and I keep turning the pile. Between those activities I haven't had a root problem yet.

 

You have two problems. What are tree roots doing in your garden?

 

I live in the country, and have lots of trees around my property. The trees are not in my garden, but they send out their roots quite far. There are two trees near my garden. That black walnut near my garden will be cut down this fall, as will some other trees.