A few curious breeding questions

Not planning to breed any time soon but was thinking about these today...

1. When you want to put a male and a female together how do you know that they are not going to be aggressive to each other? Or does that just not happen ever?

2. When you have to heat a rack, do you use one thermostat for the whole rack, and just assume the temp reading would be the same for all the pieces of flexwatt (or whatever UTH you use)? And, if you don't have a thermostat for every tank how would you know when some piece of flexwatt somewhere stops working properly? How do the big breeders do it...?

Your first question is a good question. It's happened before that a ball will eat its mate...

as for the heat, yes one thermostat for the same rack assuming the enclosures and the heat sources are all the same.