A word about shear pins- They are there for a reason. If you replace them with something that doesn't shear under excessive load, you run the risk of damaging the gear box. When I first started using an auger, I broke shear pins right and left. Then I learned. If you feel that the auger is going to bind against rocks, tree roots, or just hard clay, pull it out. I guess you have to shear a few pins before you learn. I haven't sheared a pin in over 20 years. If the auger is into rocks or tree roots, you will have to get them out by hand before you can continue. If it is hard clay, you need to soften it up with a digging bar and/or manual PHD. If this is too slow going, use water as advised by others. I've never gotten mine stuck in a hole. I guess knowing when to pull it out has served me well and it just takes practice to recognize the signs. Take it slow at first as you learn and build confidence.
athe ground around here gets really hard during the summer. My PHD will usually dig it but its slow going and if I'm not careful the hydraulic downforce on the PHD will pick up the back of the tractor...which is a bit unnerving.
pull the auger out frequently. The first time I used my PHD, I got it stuck down in the hole, and it took me a while to get it back out.