might be a long post but bear with me. it's along Mavericks path

I lived in England for a few years and one sat morning , with a hangover watched the racing broadcast on BBC. The commecntator asked his offsider , who happened to be John Francombe , fairly famous jumps jockey in England , what we needed to look for as the track was wet.
He said that you needed to look for a horse whose front legs had a loping rounded type action , not short choppy ones. I was sitting there thinking , that's bullsh*t. Anyway, I decided to play along. So the cameran showed each horse in isolation cantering down to the start. I watched all the horses , and watched the horse he said he thought would win. And sure enough it did. Admittedly it was in the market , 5/1 or something. I was thinking , Geez , maybe this blokes onto something. So I turned the sound down and put his theory to the test , and I think I picked the next 4 out of 5 winners. Most at ok odds. I was sold.
I came back to Oz , went to newcastle races one of the carnival days ( by myself, no distractions , and sober ) when it was wet. i think I won about $1000 the first day. The next day I only won about $300 . I haven't used it much since as I don't go to the races too often , and usually its been dry. I did pick the first winner on Epsom day , because of it. Then drank too much to pay attention. This is usually the main reason I don't get a proper chance to use it. It has worked on other days. eg , I backed horses I did not like on form etc because of it , and they shouldn't have won but did.

One of the main reasons it's hard to use is so many horses get taken to the barriers by the clerk , or they walk for the first 200m , and you don't get a good chance to check their action. Or they go the opposite way to the barriers from where you stand.
I have of course seen horses with short choppy actions win in the wet. So it isn't foolproof , but in my experiences it has given a good guide where you might not have had one.

I did hear Richard Freedman say that horses with short choppy actions are the ones to back in the wet. I feel more confident of the loping rounded action horses now.