The squat can be a tough exercise because you don't "know" when you've hit the proper depth. To fix that issue and avoid having someone call out the right depth for every rep, set up a band going across the power rack so that every time you go down your butt will touch it. That way you'll learn what the proper depth feels like.

You can set the band at whatever height you want for your particular goals. It should be tight enough that it makes a straight line across the power rack, but not so tight that you're tempted to bounce or rebound off it.

Tie knots in the band or loop it around something if it's too long. At no point should you have to walk over the band with weights on your shoulders. Just step over it as you're getting into position to unrack the weight and step back normally.

Safety Note

The one negative of the band from a safety point of view is that often you have to have the safety racks set low because that's what the band is attached to. At this height, the racks are too low for safety so you either need one or more good spotters. If your gym has multiple squat racks, you can steal a second pair of the safety racks and put them at the right height.