I don't worry about most snakes except moccasins. Those buggers are mean and will actually come after people. I don't know why, but they will.
I have stepped over a diamondback before. He was on the other side of a log that was down on a trail. He was just sitting there and didn't even move when I went over him. I guess I startled him and he decided not to strike.
My buddy caught a baby rattlesnake one time and kept it in an aquarium. It got out and was behind his toilet one night when I was over there. I went to the bathroom and heard the little rattle going (he only had two rattles). I don't think I have ever jumped so high in my life. Needless to say, I killed him (with a barbecue fork) and told my buddy off.
Another buddy caught a water moccasin one night while we were out catfishing. He swallowed the bait (cut herring) and the hook. Then he decided he needed to come into our camp. That was a bad decision. My buddy got his hook back.
I have also seen a bed of water moccasins in a creek before. They were slithering around in this big black ball. That sight gave me nightmares.
We have had them try to get into canoes before too. I have heard they follow boats and get in them to rest. Then they just get back in the water and go. I had one fall in a jon boat a long time ago. Me and an ex-girlfriend were out fishing and got into the trees on the bank. He fell into the bow where she was. I was looking towards the stern and heard this big sploosh. I turned around to see ***, and instead of her in the boat, there was this 5 foot moccasin heading my way. I jumped in too and we both swam to shore. We went back for the boat the next day.
At another girlfriends house years ago, her mom asked me to come kill one in her garden. It was just a black rat snake, but she was freaking out so I killed it. I chopped it's head off with an axe. I skinned him and through him in a pond near the house. When he hit the water, he was still slithering around and that was over an hour after loosing his head.
Sorry so long, but I thought you guys might be interested in all of my snake encounters, or at least the ones I can remember.
But, to answer your question, no, snakes are not hard to kill, as long as they aren't in a position to hurt you.