pouring a footing in soft clay

OK here's my problem. I need to pour a small 6" wide footing to use for Retaining wall bricks. I am going to use the footing to hold the brick in place by making it wide enough so the lip of the brick is held in place by the footing.E.G.
______ I I Retaining wall brick _ I___ I I I__ I Footing I_______I
Now my problem is I have soft clay soil where I want to put the footing. Itwould be about 8 feet long, but I am not sure how deep I am going to have to go in order to hit solid ground. I will be putting only one row of bricks on this footing. I was thinking of driving some steel rods or poles to help anchor it to the cement. Or would a lot of rebar help.
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