Prepare cake mixes and bake according to directions (any size pans). Prepare pudding mix and chill until ready to assemble. Crumble white sandwich cookies in small batches in a blender, they tend to stick, so scrape often.
Set aside all but about 1/4 cup. To the 1/4 cup cookie crumbs, add a few drops green food coloring and mix using a fork or shake in a jar. When cakes are cooled to room temperature, crumble into a large bowl.
Toss with half the remaining white cookie crumbs and the chilled pudding. You probably won't need all of the pudding, mix with the cake and "feel" it, you don't want it soggy, just moist; gently combine. Line new, clean kitty litter box. Put mixture into the litter box. Put three unwrapped Tootsie rolls in a microwave safe dish and heat until soft and pliable. Shape ends so they are no longer blunt, curving slightly. Repeat with 3 more Tootsie rolls and bury in mixture.
Sprinkle the other half of cookie crumbs over top. Scatter the green cookie crumbs lightly over the top; this is supposed to look like the chlorophyll in kitty litter. Heat remaining Tootsie Rolls, 3 at a time in the microwave until almost melted. Scrape them on top of the cake and sprinkle with cookie crumbs. This is my addition--only: spread 5 of the remaining Tootsie Rolls over the top; take one and heat until pliable, hang it over the side of the kitty litter box; sprinkling it lightly with cookie crumbs. Serve with a *new* pooper-scooper. Note, this cake should be refrigerated when not being served.