OK, I see a few things.
You have to make sure the boot is pushed down far enough that the metal clip goes around the top of the plug.
You also need to make sure that the clip is tight around the plug top.
If you are worried about the boot coming off, use a ty-wrap around the boot and plug to hold it better.
Strain relief the wire ground so it doesn't break during the engine's vibration.
If the BME vibrates too much, you may be running a rich low end. Lean the engine so it runs properly.
Last a boot grease can be used but it is not necessary. I would recommend getting the plug on the cap more than any lube.