How would you handle....?

[NM_Ref]

wow...i officiate at a school with the EXACT same problem...lol...weird

we usually let the teams know in pregame conference to stop on whistles...not horns...

[ma_ref]

"Play the whistle...not the horn" is a sentence I always say during my pre-game captains meetings. In this particular instance, since this is a known problem with the site then I'd also let the visiting coach know about it as well, and tell them that you've informed the players to play through it. Unless they're a new coach in the league, chances are that they already know about it, but I'd still tell them anyway. 99.9% of the time I'd think the visiting coach wouldn't have a problem with it, but if they do then I'd tell them to take it up with the league director afterwards.

[Dan_ref]

Set the game clock for :15 more than the period (8:15 for example). If the horn goes off incorrectly then the period is over. If not then the kids get an extra :15 of basketball.