I built my main base on the sea shore. I do not try to make my base impregnable; in real life there is no such thing. My idea is the same as the real world, use fortifications to channel attackers. So I build walls (wooden or stone) completely around the land approaches to my base with a couple of gates. Walls can be extended a couple of meters into the shallows without raising the ground. I haven't put sny defenses along the shore. I do make sure the entire interior of my base is within the anti-spawning range of workbenches, some of which I built specifically for this property and to enable wall/gate repairs if needed.

In my experience, mobs from the Meadows, Black Forest, and Swamp biomes prefer wading or swimming around the seaward ends of walls to attacking walls or gates from land. I snipe them from the shore as they do so. Most of the time, the survivors are easily dealt with in melee combat.

Caveat 1: Drakes fly over walls. I planted two staggered rows of trees four meters outside the walls to reduce the area of the sky from which they can attack.

Caveat 2: I have been hunted by wolves but only a couple of kilometers outside my base. I don't know if they will swim around my base walls.

Caveat 3: Since raid pathing was changed in June, I've only been raided by drakes.

Caveat 4: If you plant crops,keep bees, or breed boar outside your walls in fenced enclosures, don't forget to put up a FREE LUNCH sign.