A couple sinkholes have appeared in a drainage area behind my house, which is surrounded by other houses in our neighborhood. The area is normally flat, dry, and grassy, so I used to play there with my young kids before these sinkholes appeared. I'm convinced that one is potentially deadly - it is about 2 feet wide and 11 feet deep. Apparently these are not uncommon and are colloquially called a "chimney sinkhole". It is certainly wide enough for children/small pets/maybe even me to fall into, and it could cause serious injury or death if that happened. Moreover, because it is so narrow and in a grassy area, it is nearly invisible.
The property management company that manages financial/legal matters for our HOA is legally responsible for fixing these. I've contacted the president of the property management company in an attempt to get him moving on it. The person in question was initially very responsive, I gave him as much info as I could, and he told me it would get taken care of. During later followup he initially said that he had contacted the county and they responded and opened a work order. When I later offered to followup with the county for him, he changed his story and said that an engineer from the neighborhood was working with him on it.
I called the county to find out if he was just making stuff up to blow me off. He was. They insisted that they are not responsible and would not handle something like this for my HOA. I didn't find out whether or not he had actually attempted to contact the county (presumably he didn't), but either way his initial statements were definitely a lie. I also discovered that the water management district in our area takes sinkholes very seriously (because they create an easy way for pollution to get into the local water tables), and will bring pressure on the property management company to make sure that the situation is properly dealt with (presumably including real-world legal repercussions). Naturally I am following this up with phone calls to the water management district, and theoretically they will make sure this all gets fixed.
While the water management district may be able to resolve this themselves, I intend to follow up with him (via email). My goal of this followup will be to see if in the short term this sink hole can be marked, and also to get him to start actively moving towards fixing this situation (instead of waiting for the government to start pressuring him). I would also like to yell at him for lying to me, but I suspect that doing so would only hurt my first two goals. I'm not sure what actions on my part are most appropriate and would most likely spur this person to action: "informing" him of the potential for upcoming legal pressure, calling him out for lying, or just generally trying to impress upon him the seriousness of the situation (because the sinkhole could literally kill someone).
How do I convince this person to take immediate action on something that he is legally obligated to take action on, but which he has apparently been lying to me about so that he can avoid taking action?