The incident has prompted calls from the Countryside Alliance to close a legal loophole, after North Wales Police said no crime had been committed.
The loophole was identified when Mary Wynne-Jones, a member of the Wynnstay Hunt which straddles the North Wales/Cheshire border, caught an anti-hunt activist trying to fix a tracker to her trailer on December 6.
The suspect quickly claimed to be thinking about buying a trailer and drove away.
Suspecting something was wrong, the 68-year-old searched the trailer and discovered what she believed to be a GPS tracker.
Unexpectedly, the suspect then returned only to admit to Mrs Wynne-Jones and two police officers that she had placed the tracker.
Despite the admission, Mrs Wynne-Jones received a letter from North Wales Police on December 22 saying that no crime has been committed.
It said: “I am writing to you regarding the report you made to North Wales Police whereby an item believes to be a tracker was placed on your horse box.
“Unfortunately it took a while for me to make direct contact with Cheshire officers that were there with the female to see what admissions were made.
“As the female made it quite clear that the tracker was NOT placed there to commit theft, no crime has been committed.
“I have looked at various offences but these circumstances just don’t fit any, and I am not able to get the tracker submitted to our Digital Forensics Unit.”
Chief executive of the Countryside Alliance, Tim Bonner, is planning to contact Home Secretary Priti Patel about what he considers a deeply concerning potential legal loophole that has wider ramifications.
He said: “The repercussions go way beyond hunting. It is concerning that anyone could so easily be the victim of stalking. Most would agree this is a shocking violation of privacy which could put people in serious danger. Action needs to take place to address what looks like an unacceptable loophole.”
North Wales Police said it does not comment on individual circumstances but placing a tracker on a person’s vehicle is not in itself a criminal offence.
A spokesman said: “However, a course of such conduct may constitute a criminal offence in certain circumstances.
“If damage is caused or there is an intention to steal the vehicle, they would also be criminal offences.
“For an organisation, such as the police to place a tracker on a vehicle, permission is needed under the Regulation of Investigatory Powers Act ( RIPA).
“We do not comment on individual cases, but if there are issues of invasion of privacy or trespass, then these matters can be pursued through the civil law.”