Skirt, no skirt, mud flaps, no flaps or nothing at all?

Your toad is very low to the ground. I think you should be looking at something like the Roadmaster Guardian.
Mud flaps or skirts would not prevent some debris from coming out and hitting the front of your toad.
I have the grass skirt mounted to the bumper of my MH. I have had a few chips from debris. My Suzuki is higher then I am guess your Subaru sits