Safety pins are not proper accessories...
Safety pins are not proper accessories... unless you are punk, then safety pin it up! However, if you think using a safety pin to hold your shirt together is a great idea you may want to think again.
I know that there are circumstances in which holding together your shirt with a safety pin might be a necessity... like, your button fell off, you are at work, and you have no other options. However, I can't tell you how many times I have seen women pinning together gaps on their button downs so they can wear said button down without a peep show.
Women who are plus sized or even just larger up top may tend to get gaping when wearing a button down. Your shirts may gap when you are standing, or you may not have a problem until you sit down. Either way, you have two options: try the next size up or pick a different style shirt.
If you love button downs, but they never fit right, try a Henley style shirt where the buttons are only on the top 3rd of the shirt. Also, look for a shirt with a bit of stretch. Remember though... stretch fabric is not a license to go a size down, make sure the buttons fit across your largest point without gaping. Don't forget to sit down in the dressing room before you buy the shirt, again you may not have a problem until you sit down. If you do go up a size in order to fit your bust-line or belly, but everything else looks big, take it to a tailor to see about making adjustments. If that still doesn't work you just may need to find a new style that doesn't have buttons across the bust or belly.
I know it may be hard to say goodbye, but wouldn't you rather not to have to hold together your top with office supplies?