I've got zoysia grass over clay soil. Probably 10-12,000 square feet of
yard. The house is 15 years old, and there are large areas of the yard
where the soil is extremely compacted to well below the depth a normal
aerator will reach.

Are there aerators that have longer tines/deeper penetration than the ones I
usually see? I figure I need to loosen the soil at least 6" deep.

How about worms? Is there anything I could do increase the number of
earthworms in the soil so they could help soften the soil over the long
term?

Advise appreciated.

KB