I've never used a sling when shotgunning...I carry my gun at port arms, and continually glance at my hunting partner(s). If you're fairly close, doing a bit of chit-chat as you walk, you just flat-out do not shoot past straight ahead and to the side away from your partner. Basically, a 90-degree arc, away from your partner.
Further: Stay even with your partner; don't get ahead or lag behind. Make the point to him that he is to take the same care.
All the above holds if you're spread out. Personally, I think it best to be at least 30 to 50 yards apart, so that any "mistakes" are relatively harmless.
Walking without wrecking: It takes some practice, but what you do is flick a glance downward to check out your next two to four steps. You then look ahead and around while taking those steps. You just learn to keep repeating this process for your walk. I can absolutely gurantee you that mesquite, catclaw, cactus and rolling rocks will provide plenty of incentive to mind what I say!
FWIW,
Art