The problem with many single leg exercise is that the weight that you are able to lift is far lower than your typical bilateral exercise (namely the squat). The main reason for this is not because of strength, but because of the lack of balance.
I don't know about you, but many times I have struggled doing lunges and single-leg romanian deadlifts because of my shaky balance. This results in me having to significantly reduce the weights I'm carrying although I know I could actually carry more IF ONLY my balance doesn't suck so much.
This is where cable and landmine exercises become pretty much a god send. Due to having a fixed point, cable and landmine exercises allow you to really load up on the weights without having to worry about toppling over and screwing up your back.
If like me, you don't have a cable or a landmine contraption fear not. Just put one end of your barbell in a corner with a towel underneath (to make it less slippery) and a weight plate on top (to make it stable) and you've made yourself a landmine unit.
So far I've actively used these three exercises in my training. I love how it doesn't hurt my right knee, serves as a natural counterbalance and how bad ass it feels:
Cable Split Squats
Just use a landmine unit (or stick the barbell into a corner) if you don't have access to a cable machine. You can make this exercise even more effective and torturous (if you have masochistic tendencies) by slowly descending (about 3 seconds) and then pausing at the bottom for about 2 seconds. Your glutes and quads will BURN!
Landmine Reverse Lunges
I know I've posted this vid before, but it merits repeating. This is my personal favourite and can be credited for really improving my weaker leg ( the right leg). So far the maximum I've loaded for this exercise is 25kg (plates only) but I know I can definitely load more.
Landmine Single Leg Romanian Deadlifts
This one requires a bit more skill than the landmine reverse lunges but definitely much easier to learn than the traditional single leg RDL variation. Burns your buns and hammies. Guaranteed.