Rocks in my 'tainer

[rflasck]

I'm a newbie. In the past, I've heard that 1) a layer of rocks at the bottom of containers is good for drainage and plant growth (my 18 gallon buckets do have drainage holes, however), and 2) ants and other critters do not like walking on white "dolostone." Should I put a 1 or 2 inch layer of white dolostone in the bottom of my containers to help drainage and repell insects? Will it screw up the ph of the planting mix at all?

Thanks,
Dick