Your PM can control access, or you can add security cameras to the storage room that you can remotely monitor (along with exterior and common area cameras so you can check on your property anytime).

You need to investigate...have a plumber run a camera in the line and/or determine if that part of the line is actually your problem, or the neighbors, or the city, or...

Or could I add a clause that allows me to put up some cell signal security cameras to protect an item like the AC condenser during that time? 

I'm debating between an apartment complex gate or security camera service. 

It looks like that guest may become a registered visitor soon and the noise will continue, I got a doorbell camera showing the difference in how the neighbor and I close the front doors normally vs how her guest slams it.

Just today the sewer backed up again and I had a plumber Camera the line.

Just today the sewer backed up again and I had a plumber Camera the line.

Before the backhoe business (which is going to be expensive) consider running a camera down the line starting from the clean out to determine any issues with tree roots. 

It's likely not cast iron if the house is 34 years old, but make sure you get the pipes snaked with a camera during your inspection, all the way to main sewer line.

I see a time soon coming that utilization of cameras, digital locks all networking with a central system to verifies identity for self showings is soon to be "the way" and in short order become the standard.