The French have dog pissoirs in their parks. You can seea picture of one at my website

Human 'bio-solids', have proven to carry some risk, when treated re-used as fertilizer. The waste from these animals might prove safer.

In Madison, WI where I live with two dogs, we have 'dog parks' which are designated off-leash (usually enclosed) areas for pets. Dog owners are required to pick up after their animals in these areas, but the park make this fairly easy by providing the necessary bags and special bins for dropping them in. A truck then comes by at regular interval to collect the contents of those bins. I am not actually certain what happens to it after that, but I assume it is taken to a sewage treatment facility. This system works very well and enjoys a high rate of compliance among dog-owning park users. The maintenance of the dog park facilities and waste disposal is financed through a special permit system.