object hides behind other object

Hi every one,
thanks in advance for helping me
I am creating game in unity for android. I placed two object one is a leaf and other is a sect. I put sect over the leaf to feel that sec is sitting on leaf. I can see them in game view correctly without any problem. But when i run it sect goes hides behind the leaf for some time and as they both move for while and sec comes to its correct position

Pleas help me if any one solved problem like this

Thanks

leaf and sect are 2 dimensional objects (I only make a plane in unity and apply a texture on it).
I am animating both objects by changing x offset of texture