Taking ibuprofen and gelatin are methods of doing this. If you're just spotting you might be able to make them work for you. Basically the method is to take 800mg of ibuprofen to slow or stop your period for a few hours. Don't take more than the daily limit. I've tried this and it did work so I could go swimming for a few hours without worrying. The second one I've not tried yet, but the instructions are to mix a packet of gelatin with some water and drink it down quickly. That's supposed to stop it for a while.