Larger tetras, rasboras, or danios may be the answer, like Freshy said. Skirts are easily available in most places. Skirts in general *can* be somewhat aggressive and fin nippy. Red serpaes/minors aren't quite as deep bodied, but they are also notorious fin nippers. If you like the look of them, maybe try to track down the much less aggressive red phantom tetras (the black spots are more round, less vertical bar shaped), which aren't easy to find, or their easier to find cousins, the black phantom tetra. Giant danios and roseline barbs get larger (4 and 6 inches, respectively), and are pretty energetic, but generally peaceful fish. I don't know how big the mouths on the roselines get (they're on my list to home at some point, but haven't done so yet) so I don't know if they're a threat to adult guppies.