I think you're in for an uphill battle with only 20 acres. What a buck needs, want's and demands is security. The bucks need a spot free of human activity that they can use as a refuge. You can certainly imporve habitat by planting food plots, thinning the canopy to incourage new growth but without a secure place for the bucks to bed, holding them will be difficult.

IMO your best bet is to imporve habitat and the bucks will come. They may not hold up on your 20 acres but they will visit giving you the opportunity to harvest them. (a bucks home range will often cover many square miles)