in judo theres probably more risk of finger damage as its a grappling art/sport. as for aikido, long term it will weaken your wrists. but theres risk of injury in any art, including kendo. iai is perhaps the best for reducing risk of damage. dont let it put you off though. injuries and accidents do happen but not like every week. good luck in your search. it might be best to go and watch a few different ones to find out what club and art are best for you. alternatively http://www.fudebakudo.com/cgi-bin/mentor.pl may help you