The fields for the major Kentucky Derby preps continue to take shape, leaving the connections of several horses searching for new jockeys for their charges.The connections of Rushaway Stakes one-two finishers Mr. Mellon and Wild Horses have opted for the April 13 Arkansas Derby (gr. II) and Tracemark will likely be supplemented into the April 6 Santa Anita Derby (gr. I). Meanwhile, the connections of Captain Squire aren't planning to ante up the $15,000 supplemental fee to enter the Santa Anita Derby and the Turf Paradise Derby winner is now likely for the April 6 Illinois Derby (gr. II), for which he is nominated. Mayakovsky is now "99.9 percent" likely to start in the Santa Anita Derby rather than the Wood Memorial (gr. I).Mr. Mellon and Wild Horses are trained by Elliot Walden and Todd Pletcher, respectively, the winners of three of the last four renewals of the Arkansas Derby. Walden won with Victory Gallop in 1998 and Pletcher has won the last two runnings with Graeme Hall and Balto Star.Both horses will have new riders in the Arkansas Derby. Larry Melancon will replace Pat Day on Mr. Mellon and Pletcher is uncertain who will take Mike Smith's place. Day is committed to ride Gary West's Buddha in the Wood Memorial at Aqueduct and Smith is also previously committed that day."Of course I'm sorry to lose Pat," said Walden, "but I'm very comfortable with Larry. We've had good success together."Maiden winner Wild Horses (Saint Ballado -- Waltzing With Deb, by Robyn Dancer) will attempt to give Pletcher a record third straight Arkansas Derby victory."I'm just lucky to be in position to take a shot," Pletcher said Friday. "We'd love to win it again. We've always felt that Wild Horses is a nice colt, but time is running out, and he needs to step forward."Captain Squire's trainer Jeff Mullins said the $30,000 needed to enter his Florida-bred colt in the $750,000 Santa Anita Derby is too high a price."We'd have to come up with 30 grand (to start)," said Mullins. "He's nominated to the Illinois Derby, but if he doesn't go there, then he'll probably head north to Bay Meadows."Tracemark's trainer Craig Dollase concedes the combined cost of entering is high, but said it's likely the son of Conquistador Cielo will enter the 1 1/8-mile race."It's going to cost a 'little' money to supplement," Dollase acknowledged from his Hollywood Park office Friday morning. "But as far as I know, we're going forward. He's going to breeze five-eighths (Saturday), we'll see how he comes out of it -- it should tell us a lot."Dollase remains uncertain who will ride the Tracemark in the Derby. Alex Solis guided the colt to a fourth-place finish in the San Felipe Stakes (gr. II), while Laffit Pincay Jr. was aboard for his previous 11 races, including his March 3 maiden win.As for Mayakovsky, the Gotham (gr. III) winner was thought to be pointed for the Wood before trainer Patrick Biancone announced earlier this week that the son of Matty G was "50-50" for the Santa Anita Derby. Friday, Biancone said that percentage has now increased."I will tell you that he is 99.9 percent (to run in the Santa Anita Derby)," Biancone said Friday morning, adding that, "we should know a rider (Saturday)."As of Friday, Santa Anita lists the following horses, with riders, as likely for their Derby: Came Home, Chris McCarron; Easy Grades, Gary Stevens; Danthebluegrassman, David Flores; U S S Tinosa, Kent Desormeaux; Lusty Latin, Glenn Corbett; Royal Gem, no rider; Mayakovsky, no rider; Jack's Silver, no rider; and Tracemark, no rider.Holdthehelm is listed as possible, but trainer Paul Assinesi says the son of Holdthehelm is more likely for the Arkansas Derby."Holdthehelm will have a strong breeze on Sunday at Santa Anita, and, if all goes well, we'll take him to Hot Springs," the conditioner said. "He had been scheduled to run in the Spiral (last Saturday at Turfway), but he missed the race with a popped abscess in the right front. He's fine now and ready to roll."Aside from Mr. Mellon, Wild Horses, and Holdthehelm, others considered likely for the Arkansas Derby are Windward Passage, Ocean Sound, Private Emblem, and Dusty Spike, with Guppie's Secret listed as a possible entrant.Among those pointed toward the Blue Grass Stakes (gr. I) are Harlan's Holiday, Booklet, and Request for Parole.