Honest answer? I don't know. But when my business was in a similar position (not from VCs and only about 25% of that amount), my business partner, attorney, and accountant sure did, so I know it can be done. IIRC, it was a fairly complex mix of different things. There certainly wasn't a single place that held all of the money.

I know that this sort of problem isn't new, and I know that there are a variety of ways to mitigate the risk to acceptable levels. I don't think you can ever completely eliminate risk.

Dealing with large amounts of money is very complex and really requires experts to do right. I'm an engineer, not a money expert. Your question is better aimed at a subject matter expert.

But my underlying point isn't even that these companies did the wrong thing. Only that they took a risk -- and starting a business is itself taking a risk. That's not necessarily a bad thing.

But when you take a risk, you're (obviously) taking a risk that the money will be lost. That's truly an unfortunate thing, but everyone knows the rules of the game.

I learned yesterday about CDARS.

These spread your deposits over (up to) thousands of banks, keeping each account below FDIC insurance limits. You can choose demand deposit accounts, or CDs or money market accounts if you want interest.

All accounts roll up into a single bank statement from your primary bank.

There's a couple of services that will split up your deposit into 20-different banks, so that you achieve $5 Million FDIC insurance rather than just $250,000.

Also, if any particular bank fails, you only risk 1/20th of your cash.

EDIT: I never managed $100M before however. Maybe that stops being a potential plan at these sizes.