I'm working with a rescued bird right now and have been target/clicker training. I used food coloring to die the tip of the stick blue. Also dipped the tip in just a tiny bit of honey for the first few sessions. We do 15 minute sessions around every 3 hours or so. At first he was attacking the stick. He got no reaction for being a jerk or ignoring the target. Glance at or non-aggressively acknowledge the target = click&treat. Touch it=click&treat. Voluntarily touch my fingers (no biting) = click&treat. Always come to the animal you're working with in a calm state of mind, gently assertive, and with no expectations.
Expectations create anxiety when things don't go as you hope. Animals read/feel/react to that anxiety and it can set back your efforts. What will be, so shall it be. This is the first high-intelligence bird I've worked with but I've worked with many species of damaged/aggressive animals before. Across the board all of them have responded to a calm, assertive, gentle, no anxiety mind set.