I have to think of round stones as being square stones without corners. They are not really round at all I tell myself. For one thing they all have some sort of length even though they look roundish. It seems appropriate especially in Ottawa I should 'capitalize' on each stone's length and fit them into the wall, rather than along it. They can be placed so that they lean inwards and so are wanting to slip into the middle of the wall, rather than loosen and fall out of it.
Also when they are placed together in rows they have this lovely quality of forming cradles between each pair of round stones which makes it easier for nestling the next course of round stones into. This actually can add strength to the wall as the stones not only push down but also spread out and tighten up to each other along the wall. There is a kind of dynamic energy running the length of wall, which a wall made with flat stones doesn't have. Building a wall with round stones usually makes it easier to avoid running joints too.
When you use rounded stones in a wall properly the final result is very pleasing to look at and also very structural. When I squint my eyes I can visualize an imaginary grid pattern that has been formed. The stones in the wall look like square stones without any corners.