Over the last couple of years i have experimented with wooden barriers. They must be rough sawn timber, the 'hairy' type which the slugs do not like to slide up.
First i had to identify where the slugs were hiding during the day time. The obvious place was the hedge behind the flower border. To confirm this i left a couple of sacrificial plants about 30 centimeters from the hedge. The following morning the plants had been duly ravaged and the slime trails confirmed the route the slugs and snails had taken. At this point i installed the rough sawn timber off-cuts between the hedge and the bedding plants by pushing them a few centimeters into the soil. As a precaution i scattered slug pellets around the young plants and on the other side of the timber barrier. The following morning there was no damage to the plants and all the slugs had been stopped on the hedge side of the barrier.
So far, this passive defense has prevented a great deal of damage to the plants and hopefully will continue to be as effective.