So far as I can see, nobody has asked the OP (and he didn't say in his opening post) just how far he is trying to cast!! One minute we are seemingly talking about overhead casting and the next someone is suggesting underarm casting and whilst both do a job the second is restricted to some extent by the rod length and weight being cast.
The second point is, unless I miss my guess, we are talking about an inexperienced angler who is struggling to use a system (casting to an island or whatever) that by its very nature demands considerable knowledge/experience around the gear gear he is using plus almost feel and touch to achieve perfect casting every time. Even then, I have watched very experienced anglers casting and retrieving a dozen times before managing to drop the bait in the desired position, so IMHO I suggest the OP would be better advised to approach his fishing slightly differently and in a manner that reduces the obvious stress and angst the chap is going through.
Not for on minute am I suggesting long distant casting doesn't have its place in angling, but it is NOT the 'be all and end all' of fishing, regardless of species plus the fact that with time and patience casting reasonably close to a feature (without losing tackle!) and then concentrate in bringing the fish to YOU with clever and planned baiting up can work time after time.
I don't doubt the fish on the OP's water roam around the islands but that doesn't mean to say they cannot be persuaded to venture out into open water.
A couple of weeks ago I had two anglers along from me - one casting toward trees and the other halfway into open water. The first spent more time casting than fishing and the second had a relaxed day catching a few carp without the hassle. My advice would be for the OP to reassess his method of fishing and try not to do something that is very, very difficult - even for top anglers!!
Underarm casting; This is something I do much of the time as I fish small waters where overhead casting is not required. I DO cast toward trees and bushes BUT I ALWAYS stay within what can be achieved without hitting trees. Underarm casting is an art in itself and to do it easily the balance between rod length and the weight to be cast is critical. Absolutely no point in using a short rod with small weight (most of the time) to obtain distance, but rather use a longer rod (if possible) and a decent weight with the weight being as heavy as it needs to be to obtain the distance required.
Over the past week I have used an 11' rod with 3/4oz weight to cast to some trees, landing within 3' of them most times. I could've used a lighter weight but that would make reaching the desired spot a little more difficult. Any heavier and I would've probably ended up in the trees!! It is all a question of balance (like most things in fishing) and it didn't take me 5 minutes to get it right, either!!
No, for my money the OP would be better off going fishing with someone who has experience OR forget casting toward tress and fish NEAR to them. Forget all this nonsense about 'you can only catch them if you are 6" away from the trees' and save himself a lot of money and hassle. Everyone has his own way of going about things, but if what you are doing isn't working then try something that does. KEEP IT SIMPLE AND DON'T TRY TO ACHIVE THE IMPOSSIBLE........In other words don't try to run before you can walk!!
QUESTION TO THE OP: Just how far are you trying to cast AND with what tackle?? (Just interested..)
(ps.. The above is only my opinion based on my mere 65 years of fishing. NOT faultless but it works for me. Others will have other ideas, also okay as well..
pps Roughly were do you live OP? Someone on here might be able to do a days fishing with you. Worth asking...