Hello
@weeniew and welcome to the forum
I use a Dexcom and unfortunately the risk cannot be eliminated completely despite best intentions, I use tegarderm when particularly active and find this is effective, however wearing it would not stop me from exercising, also it shouldn't in theory come off, Dexcom provide clear adhesive plasters which sit around the sensor and are useful but like tegaderm them aren't completely reliable. I would encourage him to participate in contact rugby, if one does come off then contact Dexcom and see if they will replace, their customer service team are excellent so should replace this FOC for him.