No Shows !

OK guys and dolls, time for a wake up call to you people who make bookings and don't turn up.
Your hurting us.Since we have starting use e restaurant softeware that sends texts to remind guests of their bookings, no shows have reduced to almost nothing, but the last 2 Saturday nights we have had 2 tables of 5 not show up. That hurts, so we may have to bring in terms and conditions for bookings, for example ,failure to cancel your table will result in a payment of £15 per person
or
we will hold your table for 15mins ,after that we reserve the right to let someone else have it.Any sugestions are more than welcome.
Cheers

Adrian