Whats worked for me:
1 - Take your dogs. Dog walking is a viable excuse, regardless of who you run into. In my case, the dogs have a number of uses besides the "cover story". They will warn me of anyone approaching while I have my head down in the grow, I collect a bag of their excrement from the backyard, and their hair from the vacuum bag - which I spread around the perimeter of the grow area to reduce the intrusion of deer and elk, and they will "see off" any of the larger animals I may encounter on the way in or out.
This is how I usually see bears when I have my dogs along - running like the wind!
2 - Think carefully about wearing camouflage clothing. If its not hunting season, and you're not carrying a bow, rifle or shotgun - and you're kitted out in full camo, its probably going to be regarded with a modicum of suspicion (or would be by me, at least). I find it preferable to wear muted colors (OD green, coyote tan or the like - whatever will blend best to your local backgrounds), rather than camouflage. You'll be just as unlikely to catch the eye if you are still, but will be a whole lot less suspicious while walking those last few hundred meters to and from your vehicle - where you're most likely to run into other folks. Hide in plain sight - after all, you have nothing to hide as you were out dog walking/fishing/geocaching!
3 - Think outside the box when choosing your grow location. In my area - theres very little chance of my grow being "happened upon" by a casual passer-by. However, helicopters are up every summer looking for grows - and I'd rate them as the number 1 threat to discovery, in my neck of the woods. To counter the threat, I scouted a location near the airport where these LE/Navy helicopters originate from. I've worked on crew served vehicles for nearly 20 years - one thing I have noticed is that "eyes are in" the few minutes after departing and before arrival (completing checklists, scanning interior instruments, adjusting comm channels) - attention focused outside the vehicle is lowest in those first and last couple of minutes, so I'd prefer that to be when they are flying over my grow. Again - hide in plain sight.
4 - Give yourself an escape route. If you are ever surprised in your grow, either by a person or persons on the ground, or from the air - have an escape plan ready to go. That means more than one easily passable exit from the grow - with the primary emergency exit preferably terminating in overhead cover. You will definitely receive the most sun if you site your grow in the center of a clearing or clear-cut - but security precautions should dictate that you site in the best possible location giving access to the summer sun, but being adjacent to an escape route through cover. I probably lose two/three hours of (mid-summer) morning sunlight because my site is adjacent to thick bush - but I feel thats a fair trade-off for security. I don't mean to sound paranoid - but my experience is that its the unprepared that usually are caught.
5 - If you insist on carrying a camera and taking pictures of your grow - swap the SD card after taking the photos with one that contains pictures of your last vacation, or your kids, or your dogs. Nothing says "Thats my grow" more loudly than a series of pictures on your camera, documenting the progress of your grow from seedlings - ha ha!
6 - If you pack water into your grow, do it in a back-pack and have a cover story ready. Mine is that I'm training for an elk hunt in the fall - and a water container makes a handy weight addition to strengthen my back and shoulders. I don't hunt, and don't have a license to do so - but I don't require one to help a buddy that does hunt them, to pack the quarters (meat) out of the bush.
