My opinion for what its worth on here
Out of the 6 species a dog is capable of taking 5 of them single on a regular basis FACT.
A mature red stag in its prime taken by a dog single is not impossible with the aid of accidents,injury, sickness, fences, ditchs etc etc but WILL NOT be a regular occurance IMO.
Two dogs at the top of there game are capable of and WILL take red stags.