Could be it is luck of the draw, as I never got them and I pushed for almost 2 hours!
I think, particularly with your first, that reading some good articles about 2nd stage might be helpful. I thought that the care I'd received during my birth was fantastic, but when I think back to it now, I wish I had've known more about 2nd stage. Mine was heavily coached, I was pushing so hard I literally burst loads of little blood capillaries in my head, and it was all directed pushing, rather than just following my body's lead.
Sounds just like my labour, I was pushing for nearly two hours too and I pushed so hard, *TMI warning* my bum like, popped out the wrong way? The midwife stuffed it back in with her finger.

Ok back to the subject at hand, I've never heard of any way to prevent them or even to get rid of them, besides surgery.