Is there a natural way to make my tooth enamel stronger other than taking fluoride supplements?

See below. It would be better to use Fluoride rinses than oral fluoride.
Some other things: All my colleagues gave excellent answers. I would just like to add some items to avoid that many patients use not realizing their destructive effects on tooth enamel: sports drinks (very acidic), fruit rollups (very sticky sugar), breath mints, (high sugar in contact with teeth for long time), and all similar products.
Strong enamel. You should not take Fluoride supplements. It will only be incorporated into the enamel while the enamel is forming. You may use Fluoride in a topical application. A varnish type will work the best. There are other treatments as well. Use a "re-enamel" or a "re-mineralization" tooth paste. Sealants can provide a protective coating for the chewing surfaces of the teeth.
Yes. Keeping enamel stronger is done by keeping your oral environment neutral to basic. As soon as the mouth becomes more acidic ph of about 6 and below the minerals that are keeping your enamel strong begin dissolving from the tooth. Keeping your diet healthy -lots of fruits and vegetables vs juices and junk food- will naturally help your teeth. Xylitol use can help reduce acid producing bacteria.
Balance Diet. A balanced healthy diet is the best way to maintain healthy teeth. Decrease foods and drinks that are high in sugar. Also avoid frequent snacking, people that snack tend to get more cavities. I would also like to add that Fluoride is a natural substance , it is on the periodic table not too far away from calcium.
Natural. Understand that Fluoride is "natural." it occurs naturally in the water supplies of many of our western cities. Know also Fluoride supplements strengthen tooth enamel as the tooth is forming, before it ever erupts into the mouth. After teeth erupt Fluoride treatments, rinses, and toothpastes are almost as effective, and other substances may help, but not as effective.
Maybe. Theobromine (a substance found in cocoa beans) has been found in some studies to strengthen enamel. One company even makes a toothpaste (theodent) that contains it. More research is needed to know if it really works (limited animal studies and no published studies on humans yet) or if it will eventually be proven to be nothing more than 'snake oil'.
Topical fluoride. For adults, topical Fluoride rinse after brushing and flossing is most effective. Fluoride supplements in the diet are most effective when given to children ages two to twelve during enamel development. After a tooth erupts into the mouth, dietary floride is not as beneficial as topical fluoride.