lavender cuttings ?

i have three recently planted french lavenders and one plant (type is unknown) that is three years old.
i would like to take cuttings from them for future use.
i understand i shouldnt take cuttings in the first year and checked on internet site, two sites advise different ways, one is take 8 inch cutting by tearing off from
the end leaving a heel on the cutting.
the other says use a sharp knife and take cuttings between 3 and 5inches long.
first says use rooting compound, second says you can but you dont need to.
can anyone help me choose which to do?
incidentally, regards my frogs. there are loads of very smallfrogs keep showing themselves, i dont have a pond but left the saucer off one of my pots which is
about 9 or 10 inches across full of water and it seems to have what look like tadpoles in it .if not, hell knows what i`m growing out there
stan cotter