We hammered substantial angle iron posts (1.5m long ) into the ground and then attached lock boxes to those (used short bolts with a security fastener head). not a perfect solution but we hoped it would be enough to deter any casual thieves who might then have to carry the whole lot a considerable distance. We considered knocking a second post into the ground at a 45 deg angle that is then attached to the first post to make it harder to pull out of the ground, but in the end decided that was overkill, essentially if someone really wants to steal a camera they probably will, particularly if the come equipped rather than stumble across. We had no cameras stolen, but then they may not have been at much risk anyway, it was just a precautionary measure.

If there is mobile phone reception at the study site then using different cameras with a built in SIM card might be an option, that way if you check the photo e-mails regularly you might get warning that it's being stolen, and may even get a shot of the thief, or if you have the SIM card number registered for an online tracking service, you, or the police might  be able to find where it ends up or at least where it was heading.

Thanks, Steve. I have been thinking of droppers too. Ultimately, as you say, we cannot stop them, only discourage the casual thieves. A determined person can take the traps regardless of the precautions. Mobile reception, I'm afraid, is not reliable enough out here.

Concealing your camera might be a better option than securing it.  I have had some success concealing remote cameras and other hardware in artificial rocks hollowed out to enclose the device,  The "rocks" are constructed out of  insulation spray foam applied to a form the size and shape of your camera with an opening for the optics.  This is then painted to match surrounding rocks,  This technique works in my study area, but might not be an option for you depending on your local conditions.  Good luck!

Hi Eric, That actually sounds like a very good idea! I might have to play around a bit with the advanced concealment idea (going beyond the concealment from animal eyes). I will certainly see how insulation spray foam could work out here.

I don't know your study design and GSM coverage, but if you have an option for placing them above 2.5 meters above the height of the eye, looking at the ground or path, it can take less attention than the usual placement because people mostly look at the ground or forward while walking on a path or trail.

Another option, you can use spy cams at hot-spots of thieves and detect who stole your camera traps (https://www.trailcampro.com/pages/how-to-catch-a-thief). 

Good luck!

The best way is to trap the thief with another CamTrap. Hopefully you may find your cameras and stop other thief.

Using GSM enabled camera traps, having spy cameras at canopy of trees and concealing camera traps are all good options but may vary according to study areas. Sometimes you can just mention with your cameras that you are being watched then many people who don't know about camera traps may not try to steal them. Using combination all above methods can help you to reduce risk.  

Although I can't afford putting more cameras out there to spy on the existing cameras, I have considered putting up signs saying the camera is GPS tracked and being watched (even though it isn't). My big fear is that makes the temptation to steal even bigger (the "do not push" button is enlarged, so to speak...) I'm currently experimenting with making fake rocks to hide the traps in. Will see how that goes!

 You might find some inspiration in the link provided below.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4384941/

There is no perfect method against experts thieves. Therefore I agree with Eric and Huseyin and I suggest you to focus more on finding places where people do not pass and less on finding the thieves. If I were you, I would completely avoid the areas where your cameras were stolen. You can use warning messages like: Video supervised area!, but the results are not always satisfactory. Saying the camera is GPS tracked is a bed idea. Good luck!

We used a modified lock of this http://www.instructables.com/id/Trail-Camera-Lock/

It was a success as we were able to retrieve all of our camera traps. Before, we lost 5 camera traps to theft. It is lighter than full metal lock box and cost us less than USD 4 for each camera trap. However, it requires sturdy trees or some strong poles to be effective. Hope it helps!

Thanks for the home-made tips too. We're now experimenting with a simpler home-made option, just drilling cameras into thick poles (which we have to dig in ourselves in the grassland habitat). And we use screws with specialized tips, which might deter casual theft. Serious thieves will probably take down anything...

Its a problem for most of us using camera traps. Never met someone who hasn't had a single camera trap stolen in the field. I would love to hear how well your new setup works. Might be helpful to us. Good luck!