How do you defend with these units?

[Fisherking]

I had one a bit like that.

I had two militia and a light foot. I may have had more armed citizenry though.

I was lucky enough to get an area next to the town with a walled off area. I had entrenchments too.

The light food did most of the work running back and forth in the area to take care of the next threat.

I had one armed citizenry rout but they came back and I put them in a building helping out the militia that doubled as my general.

Once they exhausted them selves in the attack I just moved out to take on the cannon. It just routed away.