[thomk]

Document the truth.

If you are employed and a product owner is required to give you your workload, you are kinda of stuck. The best you can do is illustrate (over time) that you are unable to get things done because of changing priorities.

Put together a collaborative document where you write what you understand to be your tasks. When a task changes or a new one is added, add a new entry with a date/time. Invite him to see it and ask him to bookmark it because you want to be clear on what you should be working on.

This is a good thing to have around review time as well, because you may be confronted with 'It doesn't seem like you are very productive'.

Also if it is possible that your priorities are not changing as much as you thought, this is a good exercise for yourself as well.