Hello Not a Buffalo. Nice to see you around.
Good pic - I looked it up in my book - I think that's a 'Pope's Pit Viper' which grows to 80 cm and is described as '
venomous and dangerous'. Your pic is exact to my book pic ! There's at least 6 different kinds of pit vipers - some are brown but the green ones have brown at the tail. Easy to confuse with grass / tree snakes but that's a 'Popes'.
When I had a big garden - I always killed these for obvious reasons. I found one under a bucket inside a bucket once. Very nasty. You just don't want these hanging around. Being graphic about it, the blade of the spade behind the head works best as you saw

I used to find several rat snakes a week but just used to 'drive' them back out the gate - they follow the garden wall with me banging the spade behind them, (ratsnakes are no problem). Also found a cobra and a blue krait, but only once I'm glad to say.
Johnnie - your pic - that's a rat snake is it not ? They move quickly when chased - if cornered they can rear up - cobra style - the bite is dirty but not venomous.
ATB