This Young Horse is learning how to jump different colour fillers. Firstly he jumps over the rail until he is completely confident at that. Then the white square blocks and then the curly blocks are introduced UNDERNEATH rail he is already jumping.

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Note the wing on the right and the rails on the left - making it difficult for horse to see any alternative to jumping over the fence

The polythene wall is gradually introduced UNDERNEATH the top rail. This wall is particularly good for young horses as it is virtually impossible to injure himself on it.

Mission accomplished - Pony has had good experience and realises that whatever is underneath the rail is irrelevant !!!