I knew I should have clarified that. I live in the middle of a city. Most of our hiking is done on urban trails or in the very near suburban parks. The law around here is that you pick up after your dog and cart it out. Whether that makes sense to you or not, I'm sorry, but encasing dog crap in plastic is what you do or you get a ticket. Personally, I'll pick up whatever it takes to keep dogs permissible in well-visited parks.
As for the LNT thing, I never said "pack out your own poop", I said "bring extra ziplocs". Packing out toilet paper, tampons, and other waste-related waste is part of the LNT guidelines; so is digging a 6-8" cathole 200 ft from a water source to use for solid waste.
By the way, the largest ziploc I could find on a quick search was 13x18" 6 mil thickness. Perhaps that would suit the needs of AlanB's horse. Thirty cents each but you have to buy a case of 250.