place hold as

Is this the way to formulate this? Should I say 'as a guarantee'?

"We will place authorization hold on your debit card as [a] guarantee insurance"
Could I ask for you credit car Sir for an authorisation hold?

How would I have to use 'insure'? I know it isn't very polite but grammatally speaking, should I use the subjunctive?
"We will place authorization hold on your debit card to insure for you to pay for everything."

Thanks