if anyone is having this problem looking at there map. look at a map in your inventory and watch as the one in your inventory and the one in the item frame render. this has happened to me before and all i have to do is look at my map.
sry had to edit. left some thing out.
1
Basically you have your typical area dugout for your moat. instead of filling it with water, place water source blocks into your wall, 2 blocks deep, with a sticky piston in the 1st block holding the water in. repeat this every 2 blocks width wise, and redstone it all up to be activated with 1 lever to release all the flowing water into your moat trench.
personally, i have the water source about 3 blocks above the 1st layer of the moat. All the flowing water will help keep spiders from jumping over your wall. course the easier solution to spiders is just placing a stair block about 3 blocks up from your outer wall, but this looks cooler to me
you could use lava, but it just flows really slow and doesn't spread enough like water.