I know this shouldn't be a concern...

[Cricket]

Hmmm.... well, I could tell you not to worry about the poo, but you know that already.

Try asking your midwife or husband or birth coach to have you pant when you feel that need to push. Ask them to breathe with you and talk you through it ...(contraction starts, you want to push) "OK, Bec, pant, ha, ha, ha, ha, you're doing great, ha, ha, ha, ha.... (contraction ends) perfect, breathe, relax, you're doing beautifully, this baby is just a perfect size for you...." (Have a look at Gloria LeMay on pushing, by the way). She recommends panting through your pushing until the "ring of fire" feeling passes. She says that gives the time needed for the perineum to stretch, and the pressure from the baby's head numbs the area then too, making delivery less painful.

And, you can ask for a warm/hot cloth to be applied to your perineum at pushing. This does a few different things -
1. It helps relax and stretch the perineum, decreasing the likelihood of tearing.
2. It supports the perineum, decreasing the likelihood of tearing.
3. It helps direct your pushing, making it more effective.
4. It covers up any poo. A quick switch of the cloth, and no one's the wiser. Nothing on the floor, no mess, no worries.

All the best for a great birth!