The horn on my Clio stopped working too. Replaced it with one from the scrapyard, which also stopped after a little while. Then another replacement bit the dust too, before my fella realised what the problem was. Where the horn is originally mounted was allowing water to splash up and into the horn, eventually causing it to stop working. He found another mounting position for the horn, further up towards the bonnet (I'll post a picture if anyone's REALLY interested...) and we've had no problems since.