Divorce (or so I'm told) actually can negatively impact your credit score so that isn't a fabrication.

A custom fabricated job out of a full slab would be more. 

They had "fabric" over the shiplap. 

Or do you have the technicality to fabricate and install metal roofing tiles and clay tiles?

@Fabrice FortuneHi Fabrice, Welcome to the wonderful world of real estate!

You could burry the drain under some of the rock but you must put landscape fabric over the top to keep it from getting clogged by the rocks or dirt. 

But beyond who should pay is actually the issue of whether or not there is a problem or if it's a fabrication.

Clean the back of the carpet with a good bleach solution (don't get it on the fabric), clean the floor, and plan on putting your own vapor barrier over the floor at some point in the future (i.e some type of solid vinyl floating floor or similar).

Set some traps with poison, keep them filled all the time, mice problem will be solved.Did your pest guy find signs of mice, do you think your tenants may be looking for a way to justify breaking their lease for other reasons.IT is not unusual for tenants to fabricate problems prior to a planed midnight run.

You could also have a carpenter fabricate something for you as was mentioned above.