How do you tag juvenile iguanas?

I am currently working at the iguana breeding station on Utila island off the cost of Honduras, but there are some improvements to be made. They are having a hard time keeping track of the population on the island due to the tagging method. Tagging the adults is the easy part, you can simply put a band on their leg with a unique number. However, as a breeding station juveniles are released into the wild after being hatched and cared for at the station. I am trying to find out a better method of tagging these juveniles so that the station one knows that its one of their iguanas, and two it also allows them to know the juvenile survival rate. We need a system that will one mark the iguana with a unique number and possibly color to differentiate it from the wild igunanas, but it also needs to be something the juveniles won’t grow out of and won’t become a hazard. So, any ideas?