Sink some beer traps in the ground at regular intervals, fill each night and collect the slugs in the morning.

Go out with a torch at night, pull the slugs and snails off the plants and stamp on them.

Beer traps work but you do need a few of them all over your garden.

Slugs and snails need damp places to sleep and rotting things to eat (they do prefer to eat rotting plants though it does appear the opposite most of the time!). So search under stones and large bits of bark etc. Remove as much dead material and keep borders as light as possible to help dry them out.

Watering at night does make the perfect environment for slugs and snails - damp areas to walk over in the cover of night, so try to water first thing if you can.

They also seem a bit partial to cat food - my sister puts out some cat food for a feral cat and the slugs raid the saucer its in - you could use it as bait to catch the slimy critters