Inside of your home? If you wish to remain in survival mode, you can increase the spawn rate in the general area through conquest. (Keep in mind that conquest decays over time, so you'll be forced to kill mobs in the area to retain it.) If you're willing to enter creative mode, you can place an NPC respawner, which is arguably the much easier option, seeing as to how you can configure things such as NPC type, spawn rate, and spawn distance.

The best way in survival is probably to just hire some orcs and stuff, and put them on guard mode, as no enemies of Mordor spawn in Mordor.

^^^ This would indeed be the better option for survival, and it's nice because it also gives you the option to set a wander distance in blocks.