Fill in the moat with stone and hoe until it's the size you want or build a bridge across the moat with a gate at each end.

Here's mine. Not that big or fancy but it's kept many a Troll, Fulings, Blobs and Lox out. I've had to rebuild the outer gate a couple of times but nothing has gotten through the inner gate. Maybe it'll give you ideas to pursue.

https://steamcommunity.com/sharedfiles/filedetails/?id=2839440086