Wire has been tied at neck height on a popular cycling way in an effort to “hurt or scare people”, police have said.
It was attached to trees across the track in Brynmenyn, Bridgend, three times in April.
Police have increased patrols in the area, believing a jogger, walker or cyclist will be seriously injured.
Officers have also visited local schools, believing the culprit may not know the seriousness of the action.
Sgt Jonathan Ridd said: “We have had a number of calls and it’s clear that somebody is out to cause hurt or to scare people.”
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