I wish to have dynamics play out and at times to have some objects disappear behind other objects for compositing.
For example, I have a 3D ball be thrown over a fence from a 2D video. I would usually place a plane the same size and shape of the fence that would only hide objects that pass behind it when obscured from the camera view.

I found a way to almost do this with centileo, however, I get some odd reflection from nearby objects I cannot get rid of.
I have a plane I made into a shadow catcher to block this tank, as an example, and I want to hide the tank (or any object that is also behind that plane). I get my result except look at the soldier in front of the plane; he is casting a reflection I cannot get rid of. It is not a reflection property on the material (I removed that and it did nothing), and changing any setting under the diffuse does not remove the reflection.
Any ideas?

I would normally apply a shadow catcher to a plane like this and use a compositing tag to hide the object from camera.
I tried having no HDR Sky to light the scene and there is no reflection anymore, and the object is invisible behind the plane. So it is something with the HDR.

EDIT:
by going to the HDR sky tag and putting matte shadow weight to 0.01 (0.00 removes the plane and makes it totally black but not invisible) I am able to get the plane to be invisible as well as any object behind it.
There is still a small outline of the plane in AE, but I can maybe manage. A tag to uncheck and makes things hidden from camera would be nice in the future.