No ocean draining guardian farm

Ianxofour's guardian farm, the version where you never drain the monument. The spawning area is left flooded and the guardians are pushed into nether portals, so they pop out in the nether, fall down a portal elevator and die in a chamber at the bottom while you AFK. Because the kill happens in the nether, the ocean stays where it is and the whole build takes under half an hour once the materials are gathered. It gives prismarine and XP at the same time, and the drops can be doubled by having a second player kill in the nether with Looting 3.

Guardians going into the portal and never coming out is the common failure. olesandnes7501 fixed it by replacing the scaffolding in the nether room with vines, and two others confirmed it.
Items stuck at the top of the drop shaft mean the guardians are entity crammed in the nether. Ian's own fix is making the nether side one block wider, with more scaffolding and one more fence gate.
Jawt4010 had guardians dying on the iron bars from fall damage before they reached the kill chamber.
Do not use fire aspect. Guardians that die burning give no XP and looting does not apply.
The lily pads are only there so you can build off the water surface instead of pillaring up from the sea floor. They are optional.
Bring armour and food. The elder guardian hands you mining fatigue while you build and the guardians' thorns hurt while you kill.