I have chows, not labs but mine really like their nylabones, bully sticks, and homemade fleece braids.

I bought a bunch of fleece from the crafts store (like $3 worth and I still have more), cut it into strips, and braided the strips together. My two like to chew on it and they are actually quite strong. They also like to see how far they can pull the ends until it finally snaps. They did figure out that if they get it too wet, it snaps quicker which is no fun for them.