When borrowing from 401k for rental properties goes wronge?

[KANE WHITESIDE]

Hey I m looking into taking a loan out from my self directed 401k to purchase some rental properties,  I am trying to be as carful as possible by planning for the worst case scenario.  I was curious if those who have used this technique for purchasing rentals have came across any situations where some one has done this and things went wrong with renters not paying or something happening to the property, just anything that might go wrong, and how I can protect myself from anything that might put my $401k in jeopardy?