slipping a holly bush

It is possible to root cuttings from a holly, but it is not easy. You will need to take cuttings from the first flush of new growth after it has hardened. Treat them with a rooting hormone and keep them moist. It may take up to 3 months to work. The usual method of getting baby holly is from runners.

John.

some holly seed themselves all over the garden, keep a look out when weeding, I must have pulled up over 30

I have been trying to get Hollies to root from cuttings for a long time without success. You really do need heat and a misting system to have any chance. Seedlings are ok for the common Holly, but hybrids do not come true.
Having said all that, the Japanese Holly, Ilex crenata and its various forms are actually reasonably easy from cuttings.