As Sally says
. I tend to use my body to crush the relevant sheep against the hurdle, with one knee in front of the chest, and their backside pushed into the corner, second knee above the back leg. Pushing down a bit on the shoulder with a hand or elbow helps quiet them too, and stops them from jumping upwards and poking your eye out. Your last hand is for holding onto the top of a hurdle so you are secure. Then your third and fourth hands can do the task you're trying to do
I've found that when handling Hebs, get as many as possible into the pen. Our handling pen is made of hurdles, so once the sheep are in, we can shut the pen down so they are crammed. Then there's no chasing them round to catch them, so they are much calmer.
If you can handle them calmly throughout, they are more easily manageable. If it's been a bit chaotic getting them in, then go away for 10 minutes to let them settle, before you go in amongst them. Calm, firm handling, no sudden movements is the best way. Also, not looking them in the eye, and approaching them sideways or even backwards can catch them unawares.
Finally, a Heb is easier to handle when it's tipped ie sat on its bum, leaning against your two legs. Then just one hand on the breast bone, pressing down a bit, will keep them still. I use this method for injections as well as feet, as if you bend up the chosen leg a little, then the needle will slide into the relaxed muscle much more easily than if the sheep has its muscles tensed trying to get away.
Someone should run a course on sheep psychology