I rescued my horse, Ed (Sergent Fluff) from Ireland 5 years ago, I have re-trained him and spent all the time I can gaining his trust.
When we first got him, we couldn't get anywhere near him for at least 3 months. In the first year we had him, I only rode twice.
He was skin and bones, sores and scars everywhere. Maggots in his feet and thrush to the point he could hardly walk. 4 different vets told me to put him down, and I'm so glad I didn't listen.
Now he has recovered, 5 years down the line, he has been 3-day eventing, competing Prelim and Novice dressage and Went to Equifest at the East Of England Showground last year, qualifying again to go this year.
Never give up on a rescue horse, no matter how hard it may seem at times. He's now gotten to the point that my 6 year old nephew is having lessons on him, and he is a shire x gypsy, so he's not a small boy!