I've thought about forsythia. It can make a good physical barrier and screen. Thought about lilacs too. Just a question of cost/time/value and finding the right spot where it makes sense to use them. I'm not up on propagating them. I think you can buy 500 or 1000 small plants pretty cheap from larger nurseries but it would take time to get well established. I'm not sure if deer eat forsythia much. I know the lilacs in my yard get some browsing but nothing severe. If you can do it cheap enough, it would be something to consider.