Your closest is South Beach if you can confidently stay up wind. If you drift down wind there are a whole load of breakwaters before the entry to Fremantle harbour and the entrance to the swan river (not where you want to be with a downed kite) Watch out for crazy dogs as it is a dog beach. If you are not confident in staying up wind head further south to cockburn or even right down to Woodies. If not head north to leighton. Or on the river Point Walter.
Thanks, I'll scope out the spots. Most ppl I've spoken to say leighton, good to get some other options and I'll take the safety advice to heart. Seeya in the surf.