There are two potential problems when growing lettuce. Slugs and too much heat, causing lettuce to bolt.
Tender lettuce shoots are caviar to the slugs, so protect. Tips on how to beat the slugs- in the veg garden I prefer either organic slug pellets, beer traps and often a combination of the two can be most effective.
The other problem when growing lettuce is that it can bolt, especially in hot weather. Bolting is caused by the long days of light and heat, so it occurs mid summer and during a hot sunny spell. Bolting is hard to avoid, especially if we have a heatwave.
Lettuce prefers partial shade and cooler conditions, so bolting can be reduced by planting in shade or providing shade cover when in hot weather. You can also improve the soil so that it retains moisture and mulch once the small seedlings or plants are established to retain moisture and help to reduce the chance of bolting . Also, regular sowing or planting every fortnight should mean there is another crop to come along soon.
Illustrated below left is a lettuce which has bolted. The lettuce is growing upwards and in a conical tower shape instead of a rounded shape. Below also are some makeshift shade structures put up during a heatwave, a large golf umbrella (watch out for windy weather,) and safer, hessian sacks. It was too little and some of the lettuce crop bolted. This was an exceptionally hot spell of weather 29 C plus no rain and its inevitable there will be casualties.
Usually I grow lettuces with little or no slug attention, because of two factors. An abundance of frogs in the garden and the use of raised wood beds made from railway sleepers, which are quite rough. Slugs dislike sliding over rough surfaces.