Also if you can't leave, you don't have much leverage. So make sure your "irreplaceable" skills are thought for elsewhere. eg. don't become expert in some in-house tools, unless it's what your company is directly selling.

That is a danger, but you can still get substantial raises.

You can expand your territory. Like you can go from being the only guy who knows how to modify the installer, to being the person in charge of builds, CI, backups. Then heading a small department on this.