Add falling dust / debris / particles to 5second shot

I have a composited shot where a sign falls down a cliff face and bounces off it - please see the attached file to see the shot. It needs to have some falling debris added (small rocks/dust/dirt) to the shot, responding to the collision with the cliff. Creative suggestions are also highly welcomed if you believe there is more work you could do to improve the shot. You will be provided with 2K background plate and 2K sign animation, I'll need to receive back an image sequence from you. Please PM with evidence of previous work in this field, intended workflow and programs you wish to use. Look forward to working with you.