You go to the bank and you take a loan of 1 BTC, in the next 12 months you have to pay back 0.85 BTC a month in the address the bank has provided you, just like you pay now in your bank account. Simple!
Renting? The same thing!

The owner and you both sign an agreement or a contract, it specifies where to pay your monthly rent and you do so every month, you have proof you have paid in the transactions you have sent. There is no need to track anything, is just like with the banks when you look at accounts, a payment from this other account was done to the one being looked over, the same with bitcoin, a x BTC transaction has come from y.
Besides, things are far more problematic right now with cash payments, you have no way to prove that you have handed someone 10 bills of $100 unless he signs you a receipt for it.

The issue you have raised is of no concern, if that would be all that needs to be solved for BTC to become a global currency we would be already there, there are far more troubling issues and hurdles before that.