How about an ornamental fountain that has moving parts driven by water perhaps similar to japanese bamboo fountains. Would allow lots of scope abstractly expressing aikido fundamentals discussed elsewhere with obviously the flowing water as ki.

Non-abstract could perhaps be mutliple Ratti style ceramic AIkidoka arranged in a circle/spiral with cups as hands that once full, tip and perform a rough semblance of a technique on another pushing their hand into the waterflow. It might be as tacky as aikido gnomes but its grist for your creative mill!