Brian, being only two high, that is not crucial, or a problem. What I would suggest is to get a 1/2 inch heavy duty drill and a bit the length of the width of a tie and drill matching holes into each tie large enough for a re bar to go through and then about one foot in the earth. Pound this through and into the earth. I would also stagger the ties so that they overlap. This should do it.
Remember, most ties still leach out creosote and will kill the grass that is around them. Try to get the dry ties if possible. Becareful when cuting ties that you do not hit a rock or metal impregnated into the tie.