Weight Maintenance

I want to slim my Quarter horse down a little bit; he's not fat, but he could be trimmer. We have a pretty large pasture with only 3 horses on it, so I think this is to blame. Anyway, my options are either to put a grazing muzzle on him for most of the day, or to put him in a stall either during the night or during the day. Which would help him lose weight the quickest/be the best option?
BTW, he gets ridden 3-4 days a week.
Thanks!

Grazing muzzle. It limits the food intake, but you don't have to lock him up in his stall which
A- limits movement, and moving around in the pasture can help lose some calories
B- isn't as healthy as pasture, and if at all possible, it is the healthiest to pasture 24-7 (for most horses at least)

I have a horse that gets really really plump. They come inside during the day in the summer because the bugs are so bad. And then he's put out at night with a grazing muzzle on. That combination seems to help him maintain a healthy weight.

Lyric has a weight issue. So, she's on three hours of pasture anything over that is with a grazing muzzle. She gets two cups (literally the measurement type cups) of beet pellets twice a day, plus two flakes of grass only hay twice a day. She gets Accel and B-L pellets daily as well. She maintains nicely right now.