Mosquitos and bugs are aweful here in the south when detecting, especially when you are around water, bushes, etc.
Not everyone is as susceptible and us larger folks tend to excrete a lot more carbon dioxide which can really attract the bugs. Some people don't attract many bugs at all, so no one solution or product works well for everyone.
When using deet, make sure you also spray around your socks and cuffs and other places where bugs can find their way into and under your clothes. And as Dan-Pa says, many Deet products will melt, corrode, tarnish or discolor plastics like buttons, detector screens, armrests, etc. I go Geocaching also, and I destroyed the button panel of a $500 handheld color GPS when I oversprayed with deet and it completely corroded the front of the GPS.
If you perspire a lot like I do, careful with deet around the face, you will sweat that stuff into your eyes and it will burn.
Happy Hunting!