High concentrated DEET based insect repellent do work best (more precise: longer) without a doubt. Unfortunately that comes at a price: besides possible damage to your health the liquid is quite aggressive to plastics. Some pieces of my hiking equipment already has made the experience. A few days ago the center console of the Toyota Hilux took a load of 100% DEET from a leaking bottle. What the stuff, time and the sun have done shows the picture. It is worth to say that the piece of plastic survived 15 years in the Namibian sun before.