Yes losing a kilt pin is a bummer and the ones with the clasps (as the one I lost had) are the most prone to becoming unclasped.

A regular check that the clasp is still closed is recommended. However you can't keep an eye on them all the time and when brushing by people in crowded circumstances such as the Royal Welsh Show where I lost it means you can't always keep an eye on it and by the time you realise it's missing it's too late!

It was a lovely jewelled claymore pin too!

A friend of mine suggested that they would be more secure using three small safety pins pinned into the underneath of the apron and going around the rear of the pin would help - I tried this with my heavy Scottish Lion Rampant pin and so far it is still there though I still paranoically check the clasp at regular intervals!

However I also found some very reasonably priced gold coloured "diaper" style pins on Ebay which have a decoration on the top plus a stone and bought one with a thistle head and a purple faux jewel which is now adorning my new Black Watch kilt - will have to get a photo done to demonstrate how it looks and the secuity of how it's attached. I would think there would be little danger of snagging and tearing especially as it is on the reinforced hem of the apron edge.