Besides using heavy irons as a platform , you can also reduce the dressing to a modified low water tie .... this is my preferred method .
Reduce the proportions by one size on the hook . Use let's say a #2 iron and tie it if it were a #4 . I like to use tinsel , floss or thin wool for the bodies on these flies and stay away from dubbing . I always omit a body hackle (following the ribbing) , it will increase the drag and slow the fly down from sinking . Quill and hackle tip wings sink faster than mixed wing or hair wings . If you want to tie with hair , use coarse hair and get all the under fur out and tie a thin , sparse wing . Fine hair tends to trap air within . For collar hackle , keep the wraps down to two max , with one side stripped .
If I follow the above , I find I do not need to use a really heavy iron to sink my fly fast .
Mike