Taylor,
I have two of these signs attached on each side of my outside gate. Even though Yazmin is never left unattended in my backyard, it still doesn't give me any peace of mind when my guests open my gate and don't think to shut it behind them! After putting this sign on each side, I've not found my gate left open since.
The Seller makes custom signs at a reasonable price also. The words could be changed to, PLEASE CLOSE THE DOOR. I hope this helps.
Attention Pets ON Premises Please Close Gate Sign | eBay