The opposite of a moat an earthen wall. I just raised the ground all the way around my base as high as it would go about 3 ft thick at the top and about 6 feet thick at the bottom.

NO door/s!!!
Just sprint and jump/run straight up and over it.

Ended up almost maxing my run/jump skills by the time I had gotten the wall completed.

Only thing that might give it a problem are flying critters and there aren't many of those.