Tim, that is pretty awful advice! Gralloch, unsurprisingly contains a serious amount of lead shards from a standard lead hunting bullet. Raptors will indeed take every advantage of such a free feast, and scavengers such as Buzzards and Red Kites will be first in the queue. However, due to the nature of how such birds digest their food makes them more susceptible to lead poisoning! Their mechanical stomach (gizzard) actually grinds their food using grit which breaks down the lead particles to a size where it can be ingested. Birds are also very intolerant to lead ingestion.
Leaving gralloch on the surface will soon get rid of it, but we should all be mindful that it contains lead, and if we wish to continue to use lead for hunting, we should attempt to minimise its effects to counter those that would wish to see it banned. Having used non lead bullets for some time now, I actually prefer them! Apart from the increased risk of ricochet which is generally accepted, the terminal effects on deer are actually very impressive!
In answer to the OP question, there are 3 options really:
1. The good book will tell you to bury it 1m deep and away from water courses etc.. Unless you have a JCB in your stalking kit, this is not really a practical solution!
2. Use a licenced waste carrier or incinerator.
3. Leave it out on the ground. This is clearly the simplest and cheapest option, but should be done responsibly! Respect public access and be discreet where you leave it! Soft gralloch will disappear quite quickly, but heads and legs may be around for months and may distress dog walkers when pooch runs up to owner with a half rotted severed deer head! Try to cover it under brambles or down an old disused rabbit hole so that raptors can't get at it. Foxes, rats and badgers will undoubtedly discover it, but their digestive system is similar to ours where lead will just pass straight through them! Anyone who eats enough game will have ended up with a No.6 shot in the bottom of the pan that refuses to flush!


Common sense really.
Good luck with the DSC 2.
MS