yoseph1998:
Would it be too much strain on the nRF chips to constantly change channels and check for traffic?
If I understand your requirement correctly there would only be a need to check for a spare channel when a new "strip" is brought into use and it would not be a problem for an nRF24 to listen for a few moments on successive channels until it finds a free channel.
However, what you really need is for all three nRF24's for a single strip to find the SAME free channel, and that is not so easy.
You mention the possibility of 61 separate fencing matches simultaneously. There are only 128 different channels in an nRF24 and I'm not sure if you can use adjacent channels or if you would need to leave every second one unused. If so you would be running right at the edge of the capacity of the system.
You also need to keep in mind that WiFi and Bluetooth and micro-wave ovens also operate in the 2.4GHz band and a frequency that seems clear now may not be clear in 5 minutes time (and vice versa).
Before thinking further about this you need to provide details of how often data needs to transfer from a slave to the master. If the update rate is low then the options available will be much wider, including, for example, one master dealing with several "strips"
Another relevant question is whether there is already a commercial system that operates like this and if so, how does it work?
...R