I just use slabs over air when the mob gets on the slab it freaks out thinking it's in the airr since slabs aren't a full block
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0 ups, 4y
I get a bunch of sand and cacti, then wait for it to grow, and then sometimes I stand outside wehn they're fully grown and before any hostile mobs die, I hit them and I get exp.
I really like to add a fence around my house, then dig a trench, about 3 blocks wide with lava. Soon, I could try to use pistons to push mobs into the lava, and add hoppers to gain the loot.
One idea i sometimes use is a trench going all around my base. then when mobs see me and try to walk over, they fall into the moat, and the water carries them to a hopper system where i can kill them for exp. Not only does it help defend against mobs, but it gives me a ton of exp!