I am located in Colorado, USA.
We own a house that has a rented home behind it. There is a retaining wall between the two properties. We have checked on the county assessor's website and the retaining wall is entirely on their side of the property line, and the neighboring property is lower and was excavated to be level, creating the need for the retaining wall. Based on all of that, it is my current understanding that it is the responsibility of the neighbor to maintain the retaining wall, which is over 30 years old, wood, and crumbling to the point that there are large sections of exposed dirt currently being held up by nothing.
The problem is, despite the tenant in the house telling us that about a year before we bought the property the landlord had an estimator out to look at it, and more recently she told us they said that they'd have another estimate done over a month ago, nothing has happened. I have had to brace the fence to keep it from falling over as the dirt around the fence posts erodes away. The property management company / owner are very unresponsive and do not seem very keen on repairs based on the visible condition of the property (rotting window frames) and the tenant telling us about other repairs she has requested not being done.
I had even contacted a few companies to see about doing the repairs myself but they declined as they could not get the permits as the work would not be on my property. I have set aside some money to cover probably the entire cost of the work, and definitely half, but as this is a rental and therefore the owner is profiting from it, I would only want to help pay for their maintenance as a last resort if they ask for it. There are other repairs to our own home we could use that money for as well as we bought this as a bit of a fixer upper.
What options do I have legally to get them to actually repair this retaining wall before it falls?