In the lease I must receive written notice of their intention le by september 1, it was to be accompanied by a 10% deposit, half of which was refundable.

Some may require only a new checking account and the amount you deposit doesn't need to always be a lot; depends on the CU. 

I requested a double deposit ( $3700) they paid it and are still there!

@Mateusz SokolAfter the Dodd-Frank Act, the banks (entities that take deposits) really have cut back on their lending.

I talked to her and convinced her that she could tell them to move out and that I’d give her a discount for the next month while she was looking for a roommate since if she breaks the lease I’d be using their security deposit for associated expenses and she’d be on the hook for the rent until I found a new tenant.

You'll strengthen cash flow, have cash buying power for continued growth and open up 2 more slots for more property.

Personally, I like having a business account with an institution that has enough branches that I can easily utilize it from multiple locations and that my tenants can use for depositing rent. 

She deposits it directly into the bank.  

A furnished home allows for 3X security deposit compared to 2X for an unfurnished home.

What would be the transaction to account for deposits when initially buying a property?