Get a heap of sump oil and lay a trail around your perimeter.
If you need to kill a snake humanely smear a little tar from a tobacco pipe in it's mouth, virtually instant, then you have a dead snake to take to the hospital to show what bit you

Snakes can be a real problem with dogs. I had one killed in SA. She was running from bush to bush to keep her feet cool. One she chose had a cobra underneath it and she was dead before I could get back to the vehicle.
Her successor, staffie, killed a puff adder in front of my eyes but on another occasion I observed him barking at what I originally thought was a stick but turned out to be a Ringhals, ( spitting cobra). He was obviously aware that the ****er was dangerous.
Another thing that might work is to get some geese. Nothing seems to get past those buggers. My chooks spotted a blue tongue the other day and you would have thought it was the end of the world was on us