If your roses are constantly being eaten overnight you may have an herbivorous animal attacking the plants. This is most common in outer suburbs or heavily tree areas.
Most common animals would be kangaroos and possums and also rabbits have been known to eat roses. Low growing bushes are more likely to be eaten by rabbits and kangaroos, taller bushes by kangaroos, and climbers or shrubs can be eaten by possums. There have been cases of roses being eaten by sheep, goats and horses.
Control is one of the hardest in a rose garden. Fencing can control ground feeding animals however those attacking from above simply climb over a fence or gain entry via overhanging branches.
On the market are ultra-sonic animal scarers and barriers. Some success has been achieved by Quasia chips and Chilli sprays but many say this is short lived.