I generally look at rental properties that are already hardened up as a plus. 

Work in areas small enough that the mud doesn't harden while you are working; if you think you will be slow buy the 90 minute set mix.

You can also probably "harden" your units more by using different materials that are more tenant-proof, such a LVP flooring, use 1x4 wall cleats mounted on the studs for towel racks, door stoppers, only the necessary appliances for your market, semi-gloss paint and the same color throughout, simple or no landscaping, remove screen doors and replace with plexiglass, remove as many things that break as possible, remove any pull chords on fans and blinds that tenants always break, etc.

First run it through a regular self cleaning process and clean it out as soon as it stops (don't wait or the stuff will harden up again).

Quote from @Nathan Harden: Best piece of advice is to just take a leap of faith.

But I also harden them for that. 

gclid=CjwKCAiAv_KMBhAzEiwAs-rX1PLGQCydmbBZa05cv_rqn0yRXuD8ZRYJmFPGvXQE4EhtFpvgbCZakBoCEAwQAvD_BwEIt looks like it is a clear film that is applied to the windows and hardens into a bulletproof, blast-proof (and therefore certainly little rock throwing kids-proof) shield.

🏠👍Alot of people would disagree with you, but I am in the minority and personally follow this philosophy with my residential rentals because it hardens them against a severe recession and the risk of losing the property if and when rents fall too low to support a mortgage.And my father in law is essentially retired and did so after paying off all his rental mortgages to own them free and clear.

It comes in 2 liquid parts - epoxy and hardener.

Quote from @Nathan Harden: If you are looking for cash flow, then you can't go wrong with the midwest.