A better solution when collecting security deposits is to use pre-auth for all booking durations.
How it will work:
  1. Collect pre-auth for all bookings
  2. If booking is 7 days or longer, attempt to re pre-auth on day 7 (before pre-auth expires).
  3. If successful, repeat in 7 days time
  4. If unsuccessful take full payment
In theory a significant number of pre-auth attempts will be successful and only those that are unsuccessful will result in a full payment and a transactional charage.