Strange, I'd have thought that in a country as polite as Japan it wouldn't even occur to sensei that there could be people so inconsiderate that they don't pick up after their dog when they take it for a walk... On my visit last year the roads were spotless, you couldn't see even a cigarette butt let alone dog turds, but perhaps in less touristy areas the residents are less careful ¯\‗(ツ)‗/¯