Spaniel Pup Training Questions

[fathom 2]

hi all im in the middle of training a young spaniel pup 16 months old note this is my first gundog and she'll be used for rough shooting so im not going for the full field trail polished off dog obviously i want to get the best of my dog, to date i have all basic training done sit stay retrieving stopping to the whistle not as sharp as id like it though good recall, shes flushed partridge and pheasants, my questions is id like to get her sharper on the stop whistle and if she gets in to an open ditch with room to move and i cant see her are hear her work she hunts down it very fast and gets out of range any tips on either of these problems?? she dose stop so its not a big problem would just like to sharpen it up an polish it off, hunting ditches were the dogs covered but has plenty of room plus she dose try a push on alot i find myself havin to hit her on the whistle alot anything i can do to teach her her limit so to speak and get her hunting at a steadier pace like i say its my first gundog and my first time training one so its as much a learning curve for me as it is the dog, as far as hunting ability nose working cover and water work the dog id flying. thanks in advance for any advice i look forward to your replies.