We have a lot of adders around here on Cannock Chase. I don't want to tempt fate by saying that I've never seen one but John's come across quite a number of them. It's my worst nightmare.
I was quite comfortable walking on the common behind the house as I've not yet found anything to say that snakes - either adders or grass - are found on there but today I was talking to a lady and she happened to mention that her friend's dog was bitten and killed "over there" and pointed to the far end of the common

Our vet posts on Facebook every so often that they keep a stock of anti-venom should any dogs be bitten on the Chase.
I'm always in proper shoes, or boots/wellies, and jeans when out over there.