tightening ssh

I've been reading up, and talking up, various security strategies. One thing that is striking to me in looking at logs for my servers are the endless ssh probes that go on. It appears to be one of the most common. Up till recently, I had dealt with this by using firewall rules to allow ssh access only to selected ip addresses - to all others, the port appears closed (I checked this with port scans). Now, I must change strategies. I need to give access to an associate who gets his dsl ip address via dhcp, so it's always changing. I'm not quite ready to try port knocking, so, the other suggestion I read over and over is to provide ssh on a non-standard port. So, I throw this out to the collective experience - what's your take on that strategy? Won't simple scans reveal the existence of ssh access on a non-standard port? Is this really much protection? Is it merely a question of reducing odds? -- Claude Jones Bluemont, VA, USA