Your post stated "Okay so I want to teach my horse to collect and arch his neck, but I'm not sure how to do this, any suggestions?
And he always has trouble getting the canter lead that I ask for, either it be the right or left one. I have been doing a fair bit of lunging to try and build muscle, but as soon as I get in the saddle he won't listen to my leg signals. I have tried a few things, but he won't listen? 1. He also won't listen to my leg signals when I ask him to move out?
Also when I do lunge him (I don't do it every day so he doesn't get bored) he won't stop when I say whoa or anything? "
So I'm going to address your questions - but in the order YOU need to address the problems. Also, before I start, remember that horses are like children - you need to be consistent and act/ride the same way ALL the time! If you ride with light aides one day and the next day get back into "nagging" mode he will ignore you - the idea is to get him so tuned into you that when you do something (like shift in your saddle) he reacts as he's been trained - flying change, turn, halt, etc.
1. He also won't listen to my leg signals when I ask him to move out? (This is also related to: he won't listen to my leg"). This is you first problem you need to solve. so EVERY time you get on this horse you need to a. Ask lightly for the forward - halt to walk, walk to trot, etc. The response should be immediate. If when you ask he ignores OR gives you a half hearted response (takes 1 step and stops, moves his haunches but not his front legs, etc) you need to give him a VERY STRONG boot forward. Now - here's the catch - once you kick him VERY HARD like this if he gallops forward you can NOT pull back, instead you have to allow him to leap forward into any gait as long as it's forward. After a few strides you can slowly bring him back to the gait you originally asked for. So if you asked for a walk frmo the halt and he didn't move (or didn't move much) you boot him hard with both legs, allow him to canter/gallop forward without pulling on his mouth, then after several strides you slowly bring him back to the gait you desire. Remember you need to do this EVERY time you ride or he will not understand he is expected to react immediately to LIGHT aides - not so light that he flies forward every time your legs contact his sides BUT not having to boot him or "nag" him to start trotting/etc. This also means you need to be able to keep your legs from bumping his sides when you don't want him to react - so when he's trotting nice and steady at the tempo you want your legs should be "quiet".
2. He takes the incorrect canter lead. If he is fine taking the correct lead in the pasture and on the lead line then the problem is YOU. Horses take the lead indicated by riders weight and hip position. So for left lead the riders left hip is forward and weight on the left seat bone. Reverse that for the right lead. If you have problems with pushing one seatbone forward then pull the opposite one back - in other words if you find you can't push your right seatbone forward then pull your left seatbone (hip) back. The riders (inside) leg should be at the girth - that means for left lead canter the left hip is forward and weighted, right hip is back, left leg on the girth, right leg slightly behind the girth. Reverse this for right lead canter. If you can't get it following these directions you'll need someone on the ground to tell you what you are doing incorrectly.
3. he won't stop when I say whoa - This ties into #1. You need to use standard words and/or sounds for the horse on the lunge line - horse doesn't read minds so don't assume horse translates WHOA into Halt or Stop. Be loud enough and firm enough so there is no doubt what you are asking horse to do. Also the lunge line is held in the leading hand and the whip in the driving hand - with the horse positioned inbetween the 2 hands.
I suggest the following commands on the lunge line:
WHOA - for halt.
Walk On - for walk
TTTRRRRRRooTT for trot
CAN TER - for canter
So train this by asking horse to walk forward and halt MANY times until he gets it right before allowing him to go faster. Practice whoa, walk on, whoa. If he doesn't WHOA right away then snap the front of the lunge line while loudly saying WHOA. Like in #1 above - horse is to listen and respond immediately. After horse gets walk/trot/halt OK only then add canter.
4. I want to teach my horse to collect and arch his neck. You are asking for 2 different things but the neck arch will come with collection (if done correctly). You can NOT get this working until you get #1 working, and to be honest you can start to work towards this but true collection takes a lot of time and correct training.
First stepping stone towards collection is forward. In order to collect the horse horse must be stepping underneath it's body with it's hind legs, enabling the horse to carry more weight on the hind legs.
Then once you have forward the rider must be able to have enough ELASTIC contact with the horses mouth to allow horse to go forward while helping the horse to start "sitting" more on it's hind end (bending the hocks). This naturally shortens the horses frame, making the horse more uphill. At this point the rider will need to shorten the reins, since they will be looser than normal contact, since horse will now have LESS weight on it's forehand. That will start the "neck arching" you want - which is a by-product of collection.
Dressage is for Trainers!