Not a nice subject for you squeamish humans, I know.
Responsible dog owners these days clean up after their dogs - which means perhaps an average of six little bags a day to gather up the stuff.
Now, the thing is, dog mess will of course break down naturally over time and return to the earth - but I can understand why you wouldn't want it lying around in public view until then. But sadly, many dog owners put it into plastic bags that WON'T break down and will be in landfill sites for HUNDREDS AND HUNDREDS OF YEARS.
The best answer for the environment is to only use 100% biodegradable bag which will degrade much faster after it's thrown away.
|Dog waste/nappy sack bags - 100% degradable|
I am told they are also ideal for clearing the waste from your litter trays (if you have one of those cat things!) and for use as nappy sacks (if you have one of those human babies!)