How to Make isTrigger Collider Collide With Objects?

I have an enemy whose collider is a trigger, but I still need it to collide with objects. I tried adding another collider that isn't a trigger, but that causes it to bug out. I'm not entirely sure why, but it starts shaking, moving around and spinning. I believe it's because there are objects and scripts on the enemy that requires it to not have anything to collide with. So I need a way to make it collide with other things despite only having a trigger collider. Is there a way to do this? Or at least only make it collide with certain objects?

 

Have you checked this out?
http://docs.unity3d.com/Manual/LayerBasedCollision.html

 

Yes, I've tried attaching an object to the enemy with a layer that only collides with the layers I want it to collide with. But for whatever reason, it still bugs out. If I knew why this would probably be easy, but I don't know what's causing it. Whenever it collides with the layer I've set it to collide to, it begins.