Recently in several threads I have read about ways BG circumvent dogs. Our Dogs by nature do not trust people they tend to be aloof and stand offish. They will warm up to friends only after seeing them two or three times. They will not allow a stranger to touch them with out our being present. Our male does not bark or warn he lays quietly in wait than bites with teeth and jaws capable of shredding bear hides. They are intelligent and know where the utility and the delivery guy is supposed to be. If they step out of those bounds the dogs go into instant attack mode. If your dogs tend to be friendly to everyone they meet. You can teach them that not everyone is a nice person. But that is not a topic I want to broach right now because some would be offended by the methods I know work.
I can share how we keep our dogs from being poisoned or drugged. When I was younger we had our family dog drugged. Since than I have thought all my dogs not to take food from anyone except me. To teach them you will need latex or rubber gloves habanero peppers, wax paper, wax and a variety of treats
Rule number one is you and all family members may not at anytime touch any of these items without gloves on. Not at the store not at any time. If you do you have ruined the project.
Assemble your items. Wash your hands put on a pair of gloves. Slice the peppers into slivers leave the seeds on. Be sure to keep them separate from everything else do not let them touch anything. Remove the gloves wash your hands. Put on a new set of gloves. You are being careful to not contaminate the wax with the Habanero or your scent. Break up the wax as needed and melt the wax. DO NOT use the knife or cutting board you used for the peppers remember gloves on. Now carefully pick up a sliver of Habanero dip it in the melted wax than set it on the wax paper remove the pin make sure the pin hole fills in. If not once it cools you will repeat placing the pin in another location only wax deep. Do not use the pin to smooth out the wax. It will spread habanero scent. Do this with all the Habanero slivers. Remove gloves wash your hands. Once the wax is dry. Wash your hands put on a new pair of gloves. Carefully place the wax sealed Habanero peppers in treats, use treats you normally give them, along with other treats you do not normally give them be sure to include bits of raw & cooked meat, liver works great. The greater the variety the better. Place the treats in plastic bags refrigerate. Remember everyone must wash their hands and put on clean gloves each time you or any family member picks up that bag. When the dogs are not observing spread a few around the yard not alot just a few. Have friends give the dogs these treats get strangers to give them these "treats". If you take the dogs for walks go out in advance leave some treats where they will find them. It is important that the dogs never see the treats in your hands or see you give them to anyone or drop them. You will want to spread out their exposure over time. Drop some in the yard one week the next have some one give them one. A couple weeks later drop more in the yard or along a route they are walking. Repeat, until you see that they are not taking the bait. When they do refuse to take the bait give them an identical untreated treat, leave the treated one where they can get it. If after eating the treat you gave them they try for the other tell them no but let them get it if they insist. Continue until they do not accept treats from anyone except you and family. You can do this with food as well. Treating food that is not in "their' dish and not where they normally eat
I have used this technique to teach dogs not to chew and not to take food off of any plate. My dogs can have a perfect medium rare prime rib right in front of them on a plate and they will not sniff it. Drop it in their dish or on the floor its theirs and its gone.
Some dogs may need to repeat this training periodically. To check have someone other than family offer them a treat.
Habanero are the only peppers I know that work 100% of the time I know dogs that actually like Jalapeneo peppers but they DO NOT like habaneros