Laying wooden sleepers as kerbing/edging

Laying about 70m of mooden sleepers as edging around the garden, the driving area is hardcore. The sleepers are not the old heavy duty dark railway ones, but the lighter sleeker treated type.

I was told concrete not necessary, can just dig a trench and put them in, with some lighter wood backing where they meet. However it was suggested that iron bars driven in behind them would be useful. This all sound right? Should I lay sand along the bottom of the trench or will this cause more settling and show up where they meet?