Last November, Marie Claire and Mossy spent a week training under the watchful eye of Cian at Karlswood Stables, Waterside, Co Meath.
"I liked the look of Mossy the minute I saw him," recalls Cian. "He was a nice horse but, typical of many ex-racehorses, he was inclined to rush at his fences, so our training focused on slowing him down."
The week's training consisted of a mixture of flat work, pole work and jumping small gymnastic exercises or grids.
"First off, we worked on transitions," explains Cian. "Starting with walk/trot transitions, followed by medium/collected trot transitions and then canter transitions.
"The aim was to work on altering the horse's pace, by changing pace or working shorter or longer within the pace," he says.
"It's all about teaching the horse to lengthen and shorten when you ask him to."
Trotting poles laid out in a grid pattern were next on the agenda for Marie Claire and Mossy Green. The obstacle started with three poles with a small cross-pole at the end, and later became more difficult, featuring up to eight elements.
Bounces were also incorporated into the grid, to help improve Mossy Green's athleticism and teach him to lift his front end and develop his gymnastic ability.
"We also use grid work or gymnastic exercises with various stride patterns to help the rider work on their position without having to worry about 'seeing a stride'," explains Cian.
"It gets the horse into a nice rhythm and helps to place him in the correct spot for take-off.
"Seeing a stride is the absolute basic of showjumping," he insists. "Courses are built for a 12ft stride and, while you can cope with being a bit off the stride at the lower levels, it is absolutely essential to be able to place your horse at the correct spot when you start to move up the levels.
"In fact, this ability to see a stride is often the stumbling block between being able to jump one metre 10 and being able to jump one metre 30."
Cian's training exercises with Mossy Green and Marie Claire were identical to those he uses with his own horses, from naive youngsters to international superstars.
"Depending on the horse, I will do grid work, pure flat-work sessions and spend time working on canter transitions," he explains.
"I also like to practise difficult lines, maybe some S-bends and 90-degree turns, but I will only use poles on the ground," he says.
The international rider insists that showjumping training, even at the highest level, is all about the basics.
"You will only get away with the 'point-and-shoot' approach up to a certain level," he maintains. "There are no shortcuts in this game -- you need to perfect the basics at each level before you can move up to the next."
He advises amateur riders to work on straightness, achieving a round, collected canter and improving their position.
So what did Marie Claire take away from her week's training?
"It's amazing how much you can learn from a simple exercise like altering the number of strides between two poles on the ground," she laughs.
"It might look easy but when you actually try it, it's difficult.
"I found the grid-work exercises great for slowing Mossy down on the approach to each fence," she adds.
"Usually, the minute he sees a fence, it's head up and gone -- he can't get over the fence fast enough!"
However, Marie Claire also found ways to improve her own position during the week.
"I tend to sit too far forward, which results in too much weight on the forehand," she explains. "The grid work helped me to work on sitting up much more."
Marie Claire also had the opportunity to ride two other horses at Cian's yard -- a young grey mare named Lola and a bay schoolmaster called Charlie, owned by Cian's wife, Ruth.
"I tend to sit quite deep and really ride on the approach to a fence," says Marie Claire.
"My own horse is used to me at this stage, but when I rode the grey mare, I was driving her on too much. Cian kept telling me to lighten my seat and try not to do so.
"It took me a while to understand what I needed to do, but the minute I lightened my seat, the mare's reaction was instantaneous.
"It was like a light bulb had been turned on in my head: I realised how much of an influence I could have on the horse by just sitting still."
During the week-long training sessions with Cian and his head man, Johnny O'Connell, Marie Claire also worked on improving her half-halt.
And she got the chance to watch Cian working with Blue Loyd, the horse on which he recently jumped a double clear round at the Nations Cup in La Baule, France.
"It was just a fantastic week -- a bit of a holiday combined with the chance to improve how I ride and how Mossy works for me," she recalls.
"I loved every minute of it."
Cian O'Connor offers coaching, including residential training programmes, one-to-one tuition and clinics, at Karlswood Stables, Co Meath. He has trained five Irish riders up to Nations Cup level and works with young riders in Europe, as well as keen amateurs like Marie Claire. For more information, visit Cian's Facebook page