adapt current logo for 30 year anniversary horse riding club member t-shirts

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This customer received 19 t-shirt designs from 8 designers. They chose this t-shirt design from Nur Solikh as the winning design.
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We are an equestrial foundation with members that ride their horses in free-time, not in competitions, often in fields and forrests, and with utmost respect to rider, horse, and nature, natural horsemanship.
We have an existing logo which we like a lot (see attached in .ai files), but next year we will have our 30 year anniversary and would like to allow our members to purchase for a small price a t-shirt from our club to celebrate this event.
We want a print on the front and back, this print should be somewhat recognisable compared to our existing logo and the name of our club (see attached) should be included, but we would like a 'creative' adaptation, specially for this event. Preferably a reference to our website should be included.
From a distance it should be clear that we are horse riders, so a "horse" should be recognisable. Should make riders proud to show they are a member!
Updates
Project Deadline Extended
Reason: Due to illness of member of board internal discussion still pending.
Added Thursday, July 23, 2015
Target Market(s)
horse riders - natural
Industry/Entity Type
Horseback Riding
Look and feel
Each slider illustrates characteristics of the customer's brand and the style your logo design should communicate.
Elegant
Bold
Playful
Serious
Traditional
Modern
Personable
Professional
Feminine
Masculine
Colorful
Conservative
Economical
Upmarket
Requirements
Must have
- front and back design
Nice to have
- creative adaptation, simple lines?
Should not have
- should not be boring