I’ve only ever had 2 fall off early and one of those was with only about 10 hours to go, so don’t use anything to keep them in, but some people use tegaderm or the kinesiology tape that physios use to hold them in place.
I think it may depend on skin type (ie. dry, oily, smooth, hairy, whatever etc) because they stick to me like superglue, even after two weeks its a challenge to get them off me.
Initially for the first year I had no issues at all with falling-off sensors, they all stuck like limpets. The following year every single sensor (bar two) I wore over a period of several months fell off, including all the replacements and replacements of replacements I had from Abbott. In the end I gave up and stopped using them.