oldsalty, so what my colleague said they would do is get some hot coals going on the beach and a few hours before, chop some peri-peris (as many or as little as you want), open a few cans of beer, grate a lot of fresh garlic, add salt, pepper, vegetable or preferably olive oil, the juice from a freshly squeezed lemon (I've found half a lemon is better), and a splash of white wine. No real measurements, just did it by eye. Finally, reserve a quarter of the marinade off to the side and add some partially melted butter into the reserve. Marinade for a few hours (3 max.) and whilst you are cooking, use the reserve marinade to baste the shrimp. Awesome results!
I thought the addition of the white wine was strange but a splash of it into the beer makes an oddly strange, yet delicious, twist to the marinade.
The bigger the shrimp/prawns the better in my opinion. I like getting giant tiger shrimp (prawns) and making this in the summertime over some smoldering coals. Absolutely heaven!