Reddit mentions of Dexil Limited DO NOT PET Red Color Coded Non-Pull Front and Back D Ring Padded and Waterproof Vest Dog Harness Prevents Accidents by Warning Others of Your Dog in Advance (L)

If taking your dog on a walk, I strongly recommend getting this harness and leash:

• Do Not Pet leash
  
• Do Not Pet harness
  
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  Never let your dog wander the yard unsupervised. If you let your dog out to run and do their business, be there with them or have a way to supervise their activity. Supervision is the best way to prevent anyone from interacting with your animal - fenced yard or otherwise.
  
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  I am not familiar with your state's laws, but in my state if someone comes onto your property without your knowledge or consent and they get bit by your animal then the fault falls on the intruder to the property - not the animal. There is a gray area with guests and visitors, however.
  
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  But the harness and leash display openly not to pet your animal. Be proactive and try to avoid encounters where the animal can be pinned. Look into behavioral training. The behavior could be diverted with proper training and counseling.

You can always get something like this if you don't want the confrontation of always telling people not to pet your dog. They are vests that say right on them "friendly", "not friendly", "service dog", "do not pet", etc. Depending on if your dog would be uncomfortable in a vest or not, they also sell leashes and collars similar to this as well that are reasonably priced.

You're NTA here, these people don't know your dog or it's history and it's irresponsible of them to allow their kids or themselves to approach it and touch it without your permission.