Deterring house wrens?

I have two nestboxes set up in my yard. One has a chickadee nest in it with 2-week old nestlings inside. The other is a titmouse nest that was built a week ago. Today a house wren went into the nestbox of the titmice, and I'm not sure if it punctured the eggs. I tried to cover the hole of the box somewhat to keep the bird out, but I was wondering if there are any tips for deterring house wrens. Thanks!