Hi
Personally if I have a leg of something like Venison and was cooking it with fire, a few things would first be taken into account;
the weather conditions, availability of resources and how hungry I am. Firstly the weather, the cooking technique chosen should be suitable to your needs, for example if its freezing cold and you are relying on your fire for warmth, the last thing you want to do is cover it over when cooking. During periods of persistent heavy rain, a fire pit, quickly becomes an improvised water collection point! When fuel is limited and efficiency from your fire is a must, waiting for rocks to heat up just isn't practical, of course in the dry summer months and if you have plenty of fuel, well the sky's the limit to your repertoire of methods.
So all that said, how would I cook a leg of Venison on a fire?
Quickly!
First cut length ways up the leg until you reach the bone (presuming it's skinned), keeping close to the bone, using it as a guild, draw the back tip of the knife along the bone cutting it away as you go until it is removed, this will then present you with a larger, flatter surface area, allowing the meat to cook quickly and evenly, giving a more even texture. If you really hungry start carving off strips as its cooking. Lay the boned leg, know as a 'butterfly cut' horizontally over low flame and embers, or hang vertically trussed between a reflector and the fire if you need to keep warm as well (I hope that all makes sense)
Fraser