please the answer should contain materials required and procedure.
Does the arena have a good riding surface underneath all that snow? Or is it just a dirt and grass one? If several of you spent a couple of hours you could shovel the snow over the fence and use that if it does have a surface. If it is dirt and grass then it will be slippery and frozen solid so is not good for riding on until the thaw sets in and some wind gets up to dry it. Depending on how quiet the horse is, you might get away with packing his feet with car grease so that snow does not ball up in his feet and ride him steadily on snow - say walk and trot - but given that he has not been ridden for a year, presumeably from an injury, you would be walking any way - ride for 10 minutes for two days, then ride for 10 minutes for another two days and build it up in 10 minute increments so that he his walking under saddle for one and a half to two hours. You can still school a horse under saddle by insisting on good manners and square halts etc an active walk, turns and large circles. It is not ideal but since he is not fit anyway, a couple more months will not harm him just walking around. Hopefully the freeze will have ended by the time he is ready to trot for a couple of minutes during your time. Again build this up - trotting first for about two minutes within the time, for a couple of days and then building it up two and a half minutes every other day. You might want to give him walk breaks in between the trots. Make sure as I said to put grease in his feet and ask the farrier to put road studs on and use a quarter sheet in the cold weather which will keep his back warm and thereby keep him on the ground. A cold back could cause the horse to get a bit skittish for the first few times but once he warms up he will settle down.
Are there any fairgrounds/public arenas near you? I know that at least where I live the fairgrounds often have an arena and they usually let you use it for free.
Foam core is poster board with styrofoam in the middle. Don't think there's anything you can use instead. Self healing mats are made from some type of vinyl/PVC, probably a composite, definitely not rubber - again no real substitute - I suppose you could just cut on a glass top table and replace blades more often. Rubber cement - there are scads of other adhesives out there, just depends on the purpose - in other words, what you are glueing will guide what adhesive you use.
