I've done all the double digging, trenching and general ground work associated with getting animal droppings into the soil to last many lifetimes. The same effect can be done with mulching heavily...or so I've found.
Heavy soils can benefit from mulching with coarse sand as well as muck
I'm more of a 'no dig' gardener. I'd cover the whole lot in a good four inches of well rotted farmyard manure, eventually, any soil life will drag it down