Force Lat/Long in Decimal Degrees

Since you're using text, which I would recommend keeping as well, you'll have to use form rules or custom data rules to enforce the kind of entry you're looking for. The easiest method might be to have some kind of formula checkbox that checks to see if your lat/long fields have a space in there - a simple contains([Lat], " ") will do it, since a numeric lat/long should have no spacing to it. You can display a warning or clear out the value and make them re-enter. Not perfect, but a simple reminder for your users. Depending on your level of precision that users are entering lat/long - you could also cap the length of the field. Setting it to 11 characters max for example would allow you to enter a -100.000000 type value, so 6 decimal points of precision. Doesn't do all that much, just another potential enforcement mechanism.