If you see something shimmery around a tree or garbage can keep your dog away. Chances are that it is illegally placed rat poison and the same smelly rotten meat odor that is incorporated to attract rats is very attractive to dogs,too.
In NYC hiring a licensed exterminator is quite expensive as they have to be licensed by both NYS and NYC. However, there are many places in the US where you don't have to be licensed. As a result, poisons are available for purchase on the internet. Sad to say, there are property owners and property managers who take the cheap way out and purchase these rodenticides online, lay them down and put pets and children at risk as they do not know how to handle them safely.
Here's a tip: if you come across some illegally placed poison, call 311. However, do not tell them that your dog is in danger. That will not get any action. Tell them local children are at risk. And then time how fast the City responds.