Chain guard disks work somewhat. I found that my pants still got sucked into the chainring and chain if using the big ring.

I have an SKS Chainboard on my touring bike. It works REALLY well. No chance of getting the ole tattoo anymore and I can wear whatever I want. The bike has 3x8 gearing so derailer gearing is not compromised. There are many other options for single speed. It took some fiddling to get installed. The commuter bike has one of those crappy chain guard disks that inevitably crack and break.

Two things really key for installation of this particular model - 1. Your drive side bottom bracket cup needs to press against the faced off edge of the bottom bracket. Phil Wood style bottom brackets sit inside the threads only and won't work - ask me how I know. I found an upgrade kit for my Phil Wood BB that provided an extended threaded cup and retention ring for E-type bottom brackets or chain guards. Nice!
2. There needs to be decent clearance between the big ring of the crank and inside of the crank arm. My Sugino RD2 crankset didn't have enough and I wasn't a fan of removing the the big ring to make it fit or start shaving things. My Shimano Alivio crankset has a tremendous amount of clearance. Unfortunately, the Q-factor is much higher which may bother some people. I'm a big guy so I don't even notice. My MTB has a wider stance.