Lots of loping. Then add whoa and back. Then more lope. You can also add some roll backs in to encourage working off the rear instead of dumping on the front end and simply pulling themselves along.
The horse can learn the difference between nice controlled loping and running a pattern at speed.
Half halts are a good thing to teach too. If the lope starts to feel chargy, half halt to the correct cadence.
Repeat, repeat, repeat.
There are many performance horses around here that have fantastic lopes. Yet, they can chase a can or a calf with great speed.