Thank you for the quick reply!
So here's what we're thinking, a spring loaded claw mechanism in which the 'fingers' would be closed by using a servo to wind a 'string' around a shaft. The springs would then force the 'fingers' back open which necessitates the need for the motor to be able to 'backspin' speed is probably not of the utmost importance being as we will have time to open the claw comletely as we drive across the field.