The magnet and pin fasteners hold well, but they’re not perfect. If you’re going to be dancing or hiking in brushy country or wearing your felted friends in an exposed spot like the top of your shoulder, make some protection for them!
I’ve lost a handful of creatures over the years, and except for the one on the hat that blew off and couldn’t be found again, it was generally because something caught it under the chin and flicked it off the fastener. Based on that experience, they don’t come with a lifetime guarantee, but when someone adopted a squirrel on Saturday only to have it escape on the following Wednesday, that was Too Much. I replaced the squirrel with another I had on hand, and wrote this warning for you.
I use a safety chain with the first few outings for any new design, and with any creature that I don’t quite trust for the day’s planned activity. It’s just a 20" necklace with large enough links for the clasp to take hold at any point and a brooch at the far end to clip to the garment. The chain usually wraps around the creature’s neck and belly, crossing between the shoulders to make a solid harness. The Hexapod Wasp Darter is modeling it here (with a pic of the whole chain inset for comparison):
A ribbon would work as well, and you could make an ankle bracelet or a simple leash, but make something.... For more ideas, see Harness Tips.
(Note: It used to be a 22" necklace, but the Green Wyvern liked it so well he insisted on keeping a piece. With an emerald for fastening. Small creatures don’t need that much length, but this way I can use the same safety chain for everyone.)