I am installing a 70amp circuit to a service panel. I know I need to run 4 #4 wire from the main box. Can I install a grounding rod in the foundation next to the service panel and us that as my ground wire from the main panel. Also can I use 2 #4 wire for my two hot wire and a #6 wire for my neutral wire.

Thank you

You need to be more clear. If you are running a circuit or feeder you are NOT running it to a "service panel".

Is this a sub-panel, fed from a main panel? If so then you do need a ground wire run with the feeder.
A ground rod IS required if this is in a detached structure. The ground rod DOES NOT provide a ground as you suggest. It has a completely different purpose.

-Where is this service panel going? Example: detached garage
-How far away, if it's going to a deteached garage