I love using a linked double crochet (Ldc) whenever I need a double crochet fabric with minimal holes. So here is how you do it.
1. Beginning position, ready to go.
2. Locate the center "bar" of the previous stitch and insert your hook from top to bottom.
3. Yarnover and pull a loop through.
4. Insert your hook into the top of the stitch in the row below, yarnover, and pull a loop through.
5. You now have 3 loops on your hook.
6. Finish up just as you would for a standard double crochet. Yarnover and pull through 2 loops, yarnover and pull through the final two loops.
7. Your finished stitch.
Here's what it looks like after a foundation linked double crochet row (fLdc) and 3 rows of linked double crochet (Ldc). It's a nice, unholey fabric.