^In addition to Kiwi's advice of how exactly to pick up/hold...
Stand close to the horse but facing slightly away, with your knees bent. That way, your head & other important bits should be out of range, should the horse kick, and if he gets the back of your bent leg, you might cop a bruise, but he's unlikely to do any real damage.
Keep your body in contact with the horse's body, so you can feel better how he's feeling, respond before he feels the need to take that foot away.
When you first pick up a foot, if you hold it by the toe, fetlock flexed, it's easier & safer to hang onto it if the horse tries to pull away. I'd practice doing this, and giving it back to him when he's relaxing & letting you hold it, before asking for more.