The EASIER way is to get a container of white pepper (t's much stronger) and spread it over the garbage, that works so much easier than what the other stuff is you tried. Dump the whole container, dusting it evenly all over the stuff.
Also, if you can catch them, take them over to animal control and tell AC the dogs were running at large, with no owner nearby. You can do it anonymously. DUMPING the dogs around the city is illegal and can get you jail time. It's considered theft, whereas going to animal control means the owner has to pay to get them back ($125 per animal in our city).
Keep filing a complaint with police about the trash, it's a health issue. Get photos of the dogs doing it if you can, as positive ID.