Additional requirements/money for higher-risk tenant

[Lyndal McMurphy]

I've been told that some people will charge first AND last month's rent (in addition to deposit) for higher risk tenant. For example I have one now that has terrible credit but they are blaming their ex-spouse for the bad credit and claim to be on track, make good money, etc.

Say for example I collect first and last month's rent at move-in and they eventually get behind on rent.... Say it's the 15th of month 5 and they haven't paid. How do I leverage that last month rent? I certainly don't want to just apply that to the 5th month and then just start chasing them for month 6. Can I still serve Pay or Quit notice and start the process on Month 5 day 15 even though I have that extra month in "reserve"?

Other things you've done to accept a higher risk tenant?