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Full-back Fenlon and midfielder Merrifield, both 18, have put pen to paper on deals for next season and will now push for places in the first-team squad.
Boss Terry Brown told the club website: "I am pleased to announce that we have signed two of our best young players.
"They will now come on board with the first-team squad during pre-season and hopefully they can play a part in League Two next season."
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