Not only the DEET presence, but also its level, is important in terms of the effectiveness of repellents.
In many countries different levels of DEET are permitted. The more DEET the repellent has , the better (at least up to 50% concentration, as research hasn’t proved any difference above it). However DEET can have negative effects on our health, as well as that of other creatures. It’s important to keep the right level of it and be aware of its influence on others consider the fact that every year many anacondas die because of unaware tourists who are covered with DEET repellent touching their delicate skin.
This information is not distributed widely, while it may save many creatures lives, as well as prevent spreading the diseases caused by mosquitos.
The best way of combating it would be through education and in my opinion an interactive web page would be the most effective medium.
A further development that would be useful or effective would be to create the DEET level detector to check if we still have it on our skin or should apply once again.