Trot poles and hill work could help to strengthen the hind end
There are multiple ways to help your horse engage.
First of all you need to use a lot your legs (especially the interior one), put movement ahead, do a lot of transitions (especially gallop-stop-gallop) and all of your starts from the walk.
Go backwards is also very useful to puttee weight on his back.
Do a lot of lateral movements (leg-yielding, shoulder-in for the interior posterior, haunches-in, haunches-out...)
Don't forget to be really straight and do not pull the interior rein over you because you will block the engagement of the interior posterior.
Do a lot of circles, it will help you to have engagement and your horse will rush less.
The last thing you can do that is great for your horse and you can see your faults really fast is putting two small jumps away from 7 strides and try to do 8 or even 9 strides, if it goes back to trot: you have a lack of legs and if he rushes: you are not straight enough.
I hope i could help you :)