There are two kinds of eclipses, one eclipse occurs when the MOON's orbit bring it in between the Earth and the Sun, and the other happens when the EARTH'S orbit brings it in between the Sun and the Moon. The Moon can never "go" behind the Sun, as in the order being Moon, Sun, and the Earth. The moon is the Earth's orbiting body and as such will always orbit the Earth, it never leaves it orbit and goes around the Sun. I hope this helps you out. Also, this is not exactly concrete, as a big enough object could 'tug' on the Moon and alter it's orbit. This object would have to be MASSIVE, like another planetoid or object bigger than the Moon and it's mass. That would have SERIOUS consequences for us, so here's hoping that never happens.

Another side note if you didn't know; The Earth is approx. 93 Million miles from the Sun. We are in what is considered the "best distance" from the Sun to have life on the planet and not be too hot or cold.