I call it Accepted or Rejected and we typically do it on a recovery day. I purchased a decision coin on a swim trip several years ago. They have all kinds but this one has "Accepted" written on one side and "Rejected" on the other. It is just as easy to do a regular coin with the words printed on a sticker or just call "heads" accepted and "tails rejected.
You need several (say 20) 3 X 5 note cards. You have 2 options either write a set on it yourself or hand it out to the swimmers and they write a set on it. Once a set is written on the cards you shuffle them like a deck of cards (review cards for knucklehead submissions).
You then turn over a card and read the set.
The coin is flipped. Again 2 options, the coach flips or the swimmers can flip.
If the coin lands as "Accepted" the group does the set as written. If the coin lands as "Rejected" the set not done and a new card is turned. Another option we have done is that and "Rejected" set leads to a 100 EZ swim.
I try to keep the sets small and no more than 10 minutes but some are very short. Here are a few...
*2 x 300 on 4:30 Every 3rd Length FAST NO Free
*8 x 50 on 1:00 - Odd 25 Underwater/25 Overwater, Even Back
*12 x 25 Nasal Set on :30 Nasal Set is one breath for each number in the set so 1st 25 is one breath etc
*500 Social Kick with Fins
*8 x 25 on the :20 Get Outs - Get Outs are Muscle up (hands to feet out of water, no knees no butts on ladders) and dive in on Interval
*Pull 300 BP 7 on 4:30, 200 BP 9 on 2:50, 100 BP 11 on 1:20 - BP = Breathing Pattern
*1 Round Sharks and Minnows
*9 x 50 Breast on 1:00 3 sets of 3 #1 BR with Free Kick work Tempo, #2 BR with Fly Kick work Undulation, #3 Normal BR
*50 Underwater Goal NO BREATH
*400 IM for time
The possibilities are endless. The kids really get into it especially when a easy one gets "Rejected"