Help? Inappropriate glances from father?

Help? I don't know how to deal with this. My parents came to stay with us for a few weeks and will be here for another month. In the meantime, my husband and me found out we were pregnant and I have ofcourse started putting on weight in places you put weight on when you're pregnant. For the past 2 weeks, I've noticed my father stare at my chest, even when I'm right in front of him, talking to my mom. It's not just a glance, its a creepy stare. It's to the point where I just stay in my room and don't even go out of it in my own house and eat and use the kitchen when they are not around. I spoke to my husband and he just dismissed it saying its a natural reflex for men to 'look' since its there and since I've put on weight there too because of the pregnancy. But its my father, shouldn't he have boundaries? If my doctor did that I wouldn't go to him anymore. With my father, what do I do? My husband said I should ignore it till they go back home but that's another month away. It is completely creeping me out and he isn't even trying to hide it. I wish I could just change their ticket dates and kick them out of the house right now, but that isn't an option since it would hurt my mom, who is the sweetest person ever, but completely in denial and completely oblivious. Talking to her won't help because when I had tried to talk to her about issues in the past, she had always just pretended it was in my own head. Help?! I don't know what to do. I don't want to tell him directly because it is embarrassing, to me, as well as to him, since their ticket is non-changeable and we're stuck with them for 4 more weeks. What do I do?