Can understand you being a bit miffed at the bones left lying around, i have the same problem near me and it's a daily battle to keep Neo away from them.

 I live right next to a small dog park that is ideal for quick toilet stops before going on a proper walk, unfortunately there is a family at the top of the road who have a Staffie that is never walked, they just chuck it out the door on it's own to run around where it likes and always with a bone in it's mouth which is then dropped in the park and left. They also have no control over the dog when they try to get it back in (which is usually several hours later!!) and they bring more bones out to entice it home and usually leave them lying about as well. Neo starts searching for the bones the minute we walk in there and i've lost count the amount of times i have had to fish them out of his mouth in the dark when he has managed to get them before i've seen.

hope there are no ill effects with your gang