The idiom to draw a line in the sand means to set a limit or a boundary beyond which you are not prepared to cross. When you draw a line in the sand you indicate that there are repercussions that will occur if someone fails to respect your limits or boundaries.

1. There have been too many instances of work not being completed on time. It's time to draw a line in the sand and say enough is enough. If it happens again there will be repercussions.
2. It's about time we put the issues we've had with each other to bed. Let's draw a line in the sand and move forward for the sake of the business.

1. Your father and I have done our best to support you through university but I'm drawing a line in the sand when it comes to buying you a car.
2. Our neighbour next door regularly has loud parties that make it difficult to sleep. I'm drawing a line in the sand and going over there now to talk to them.