I have very little leverage on my properties, and I offset the leverage with cash invested bonds to mitigate the little debt I have (i.e. -$200K in mortgages, +$200K in bonds).

TLDR: If you're in year 4 of 10 and pay the mortgage off, your payoff balance will be adjusted to reflect the cost of buying a gov't bond that will produce the equivalent amount of dividend payments for the remaining 6 years (in other words, one way or another, the lender is absolutely going to get their 10 years of payments).

This could be just like stocks and bonds at the end of the year.  

Also, consider that he may be rolling the cost of licensing, continuing education, and other associated costs into the permitting fee.In some situations, municipalities require specialty bonds or licensing fees.

Quote from @Tracey Bond: Looking for helpful information.

Nothing is passive and even US treasury bonds which are considered the safest investment require one to monitor the economic climate.

How about a stock, bond or other publicly traded security?

If you have loss-position assets (ie stocks, bonds, etc..) talk to your CPA to see if the year of deemed sale will be a good time to sell the other assets and thus harvest the losses.

This post says I can use a bond or surety which sets money aside to account for the lien amount and then get the lien off the title.

If you truly want something that's completely safe and predictable, it would make more sense to invest the money into bonds or mutual funds.