I don’t know about for field work particularly, but we train our competition Obedience pups to go to a particular mat (thin bed) and stay there. We can then bring the mat with us to new places and it gives them a designated spot to hang out on while not working. We usually crate them if we are leaving them alone, but for example if doing a ring rental with several dogs and you just want to switch out, or if you are hanging out ringside waiting your turn to go in and the crating area is too far away. Also useful if you are visiting family/friends and don’t want them mooching from the table as it provides a familiar spot for them to stay in.