Cardio conditioning - need ideas!

I need to speed up building up my cardio, and I need to decide how to best go by doing it. Don't really want to drastically increase my swimming, since I alerady do 2400-3000 Y or M a day (depending on waht pool we end up in SCY or LCM), and about couple times a week or so twice a day. This is all my shoulders and upper body are willing to handle without getting strained to a point where it starts feeling like a serious muscle irritation ratherthan just DOMS. Still need time to build up the strength there. I'm relatively pleased with how my strength is comingalong. My cardio really frustrates me. :rolleyes: I'm a klutz when it comes to running and don't really want to add strain to the joints etc. that running will do. Wanna save my legs for swimming. Really don't want to do stuff that will increase risk of injury that will take me away from swimming training. Now that my friend filled my head with the idea that I might have a chance to qualify for FINA master's games in Italy, which I was planning to go to and just watch my friend swim. I'm not really sure how realistic that idea is. Maybe 50/50. I dunno. I'm kind of unsure as to what would be a good choice to give my cardio more of a push, something I can do as a second workout of the day. Do I get back in the pool in the afternoons, and do some intense kicking sets with longer fins (this actually sounds like something I'd be pretty eager to do)? Something dryland? Well, this is about as far as I had thought this through (not a lot just yet). So many options - I'm not sure which way to turn. Any input, ideas, suggestions you guys might have that can help me think this through would be welcome. Or... maybe I just more patience. I'm not sure if I'm pushing it too hard or not hard enough. It must be one of "those" days today.