Whenever I squat with a challenging weight, I have problems keeping my right heel down. I don't feel like I'm leaning to the left at all, but I want to make sure I hitting both legs evenly.

What can I do to fix it?

Whenever I squat with a challenging weight, I have problems keeping my right heel down. I don't feel like I'm leaning to the left at all, but I want to make sure I hitting both legs evenly.

What can I do to fix it?

I have read people recommending to put a weight (or something to raise your heel) under you heels. I've never tried it, so I can't say for certain that it works. Only one way to find out :)

I have a similar problem when squatting. I believe it is because your calf muscles aren't conditioned to go the full ROM so you need to start doing calf stretches regularly. The heel under the plate works but it does not fix the problem. I would recommend the plate for now and start doing Soleus/Gastrocnemius stretches

http://www.exrx.net/Stretches/Gastrocnemius/FloorBoard.html
http://www.exrx.net/Stretches/Soleus/FloorBoard.html

Good luck to you

Work on flexibility through the ankle.