My favorite clean joke:
A guy is walking in a field and notices a fairly large hole in the ground. He walks over, looks down, but can’t see the bottom. He looks around, finds a small pebble and tosses it into the hole, cocks his head and listens...
Nothing.
He looks around again, and spies a much large rock, picks it up and waddles over to the hole and tosses it in, cocks his head and listens...
Nothing.
He looks around for the third time and sees a large railroad tie, drags it over to the edge, struggles to lift it up on end, and then pushes it into the hole and cocks his head and listens...
Nothing.
However, while still listening for the crash of the railroad tie, he notices movement on the top of the hill. He turns in time to see a goat racing at incredible speed across the top of the hill, hang an abrupt turn, and starts racing down the hill right towards him. He just has enough time to jump out of the way before the goat jumps into the hole. He bends over, cocks his head and listens...
Nothing.
Just then a farmer comes up and says:
“Have you seen a goat around here?”
The man says:
“Yes! He was running on the ridge of that hill at incredible speed, turned towards me and streaked down the hill and dove into that hole over there!”
The farmer:
“Impossible. I had him chained to a railroad tie.”
:)