Regarding anti-malarials, you can only take them for a set period (typically 3 months max), otherwise you will do yourself more harm than good - damaging your kydneys as referred to above. The treatment is also a strong dose of the same drugs used for prevention and repeated treatments can again cause damage. For long stays then it's a case of covering up at dawn and dusk, though essentially you are going to get bitten whether the bite shows or not is a different issue. If you contract malaria, then regardless of how it's treated you can have a relapse in the future. You should all understand the risks.