The adult clearwing moths that lay the eggs that become the Squash Vine Borers emerge from cacoons in late June to early July. I would plant my squash as soon as
I could after danger of frost is past (Memorial day around here) and use Floating Row Covers to protect the plants.

kimmq is kimmsr

My concern is larvae that are already in the ground from last year, Row covers will just trap them inside the ground where my plants are.

Sneed - Plant in a different spot.

What might be in the soil now are not larva that will be munching on your plants, they are pupae that will emerge as adults that will lay eggs that will become the larva that will munch on your squash.

http://www.extension.umn.edu/garden/insects/find/squash-vine-borers/

kimmq is kimmsr

i have had good luck covering the stem that comes out of the ground. somewhere i read this and it works. they want to lay into the stem part only, and i used some brown grass clippings and mounded over and all around. I imagine shredded paper, leaves etc would also do the trick.