If you're in the UK, most chemists have Molnlycke Mepore 7 x 8 cm plasters behind the counter, so you need to ask for them, not on display. Omnicare do them for 17p, other chemists for 40p. I normally stick one on my libre, not so much from a sensor falling off point of view, more that it just smoothes out the edges, so it's less likely to get snagged. Haven't found it to make any difference to readings. Some people use rocktape, but I couldn't be bothered ordering stuff on the internet when the mepore works for me ok. Hope you're having fun with it - these little plastic discs have made my life a hell of a lot easier!