Charlie,
Double clutching is when a female lays a second clutch of eggs int he same breeding season. This can happen in one of three ways:
1) She was bred back to a male after she laid her first clutch (this breeding does not guarantee that she WILL double up)
2) Some females will hold back enough of the previous breeding's sperm deposit to fertilize a second batch of eggs and double clutch even if she only has contact with one male for one breeding.
3) Some females will simply lay a second batch of eggs that have not been fertilized at all, and these will all be slugs.
Double clutching is fine as long as the female in question is large enough to sustain the stress necessary to produce viable eggs. Body weight of the female is the key factor, and a thin female shouldn't be exposed to a male in the hopes that she'll lay a second clutch.
Hope this helps -- Darin
P.S. What part of Missouri are you in? You can email me with that if you like.