The problem is that just deciding to carry one is not enough; just like buying one and sticking it in the drawer at home with no further thought or training is a bad idea. If you don't practice handling it, get used to it, gain confidence with it, it's entirely possible someone could take it away from you and use it on you. It's a commitment, not a whim.

Rather than using the chemical product trademarked as Mace, pepper spray has become more popular, and would be a better alternative. Pepper sprays can be bought in various strengths, too. Whichever route you go make sure to pay attention to the expiration date on the product. The closer you get to the expiration date, the less effective the spray becomes. Kimber makes a product called a "Pepper Blaster" which is rectangular shaped, has a bit of a grip, and a trigger so it's natively easier to aim and to hold than an aerosol can. Just Google Kimber Pepper Blaster and you'll find the product easily enough.

As far as defensive moves for the ladies, there's always fingernails to the face, thumbs in the eye sockets, and knees to the nuts. Also, if they grab you from behind, if you'll just rake your foot down their shin, and smash your foot down on top of theirs as hard as you can, you'll break all the little bones on top of their foot. It'll hurt like hell, distract them long enough for you to break free, and slow them down enough that you can bolt for the door.