The idiom 'to sit on the fence' means to avoid making a decision or taking any action. When you 'sit on the fence' you are essentially doing nothing and are not on one side or the other of a decision or disagreement. This phrase is often used to encourage someone to make a decision or to take action 'you can't just sit on the fence on this issue', you need to make a decision.

1. You can always trust Katie to tell you what she really thinks about something. She never sits on the fence.
2. Now is not the time to sit on the fence when it comes to discrimination, we each need to look at how we can help in these situations.

1. We can't afford to sit on the fence any longer. We need to make a decision about which direction to take with our marketing strategy.
2. I have no idea whether they will agree to our terms and sign the contract. At the moment they're sitting on the fence and refusing to commit themselves.