Long term tenants: Original Deposit vs. Current Rent Rates

[Lucero Galvan]

Hello all, I have had long term tenants (5 years) which have given a one month's rent deposit at move in 5 years ago. Now, rent is much higher than when the original deposit was made and the tenant has been slacking on paying rent. For future purposes, how would I go about having long term tenants and their deposits being less than current rents? Or am I to have new deposits every time a lease is renewed? How can I protect myself with deposits with long term tenants that can end up costing more than what they deposited?