Does anyone recommend a deposit alternative insurance company?

I know that ADU's was an alternative to building from the ground up.

An alternate perspective from someone in a larger city market - I am hesitant to put my STRs on Google maps.

What alternatives would you recommend?

I would check and see if this is something your bank offers, or alternatively a lot of PM software has the ability to do it for a small fee too. 

As an alternative, I am requesting contractors to sign hold harmless and release of liability agreements.

Not saying it cant be done or you shouldnt, just dont bank on it being a cheaper alternative. 

Alternatively, set aside one or two boxes of things that family might want that you can offer for anyone to go through....believe me, it will save you some grief in the long term with your family.  

Alternatively, you could use other assets as collateral

As an alternative, I am requesting contractors to sign hold harmless and release of liability agreements.