I advise people to put a waterproof plastic groundsheet INSIDE their tent, not under the floor as recommended by tent makers and so-called experts. An interior groundsheet will contain flowing groundwater that floods your tent.

What about using a second groundcloth under the floor to prevent punctures from rocks and sticks? Bad idea because water that is trapped between the tent floor and exterior plastic sheet will be pressure-wicked by body weight into your tent. The effect is similar to pitching the tent on a slab of concrete! Also, a second, exterior groundcloth is just one more thing to carry-more bulk, more weight.

An exterior groundcloth will not discourage tears in a tent floor. Why? Because holes commonly develop like a "green stick break". Example: When you bend a green stick it compresses on the bottom and elongates on top. The break first occurs on the elongation (top) side. Ditto when a sharp stick pokes through your tent floor: As the stick begins to force its way upward through the floor, the undersurface (non-coated side) of the nylon compresses and the upper surface (coated side) elongates. When the elongation becomes great enough, the top coating breaks and the stick pokes through. The solution is to strengthen the elongation surface (top surface), not the compression side. An interior groundcloth does exactly that.