I've heard the same about Marmite but hate it!! Actually I'm a magnet for mozzies but a few years ago I got given this tip and it's worked for me and the rest of the family. For one week before we go away, and all the time we are away, we take one vitamin B1 tablet and one odourless garlic capsule each evening (apparently mozzies hate the smell of garlic and yeast [which explains the Marmite, B1 has the same smell]). We also use the Avon Skin So Soft dry oil spray (the one in the green bottle) which I am told the US army use when in the jungle.
We tried deet once - it melted the leather on our shoes so *** only knows what it was doing to our skin!!!
We also use the lemon cologne during the evening if the mozzuies are extra bad - and it smells lovely and cools you down as well.
Whatever you use, I hope it works for you.
JAKKI