That depends. Do you intend to leave contact information with the container, be held legally accountable for its presence and the ramifications thereof, revisit the container to check on the status of the horse dung, supply a log book to be filled out by visitors to your dungpot, procure permission from the rightful owner of the roadside, and keep current data on your cache posted to the geocaching.com website?
Then no, it's not litter, it's officially a cache. Granted, I doubt it'd garner much interest unless you put something else in the box, but you don't strike me as the sort of person who gives other people anything but shit.
That depends. Do you intend to leave contact information with the container, be held legally accountable for its presence and the ramifications thereof, revisit the container to check on the status of the horse dung, supply a log book to be filled out by visitors to your dungpot, procure permission from the rightful owner of the roadside, and keep current data on your cache posted to the geocaching.com website? Then no, it's not litter, it's officially a cache. Granted, I doubt it'd garner much interest unless you put something else in the box, but you don't strike me as the sort of person who gives other people anything but shit.