Dic: fight your corner, argue your corner

▶ BrE. to try very hard to defend yourself in a discussion or argument, or to do this for someone else
▶ (British) to defend something that you believe in by arguing

• You'll have to be ready to fight your corner if you want them to extend the project.
• My line manager supports me, and says she's willing to fight my corner.

.... ... LDOCE, Cambridge Idioms

▶ argue your corner

• Working out what you're worth before you attend your appraisal will arm you with the information you'll need to argue your corner and get the wage settlement you deserve. (... http://work.chron.com/discuss-salary-performance-appraisals-2240.html ) 
• But in retrospect, it was a clarifying moment, it made me understand that it was a mistake to go down that road of appeasement. It made me clearer — no more apologies, no more excuses, no more appeasements, no more compromises. I am just going to say my piece, argue my corner, and try and stand up for what I believe in. And if people don’t like it, tough. (... ‘There is no right not to be offended’  ) 
• This has been the case for all of my working life time, so the idea that we need to argue our corner is not new. What is new is that funding agencies now demand evidence of impact, a demand that can only grow as pressure on resources intensifies. (... http://www.aontas.com/blog/2011/11/15/making-a-case-for-community-education/ )