I have strapped the mojo pole to a cinderblock before when a rocky bottom stopped me from shoving it into the ground. Worked great at the time but there could be a problem with it being top heavy if you wanted the mojo to be really high above water/ground level. It could also suck to have to carry out a cinderblock along with your gear if you hike out to hunt.
As for a flag something like this is what my cousin uses and swears by. FYI That link is just the first one that I found so if you go that route be sure to shop around. I will text my cousin to find out what brand of one he uses and edit it into this comment later.