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So, here is the solution we've found:

• The Chain Length of your calf's IK constraint must be 2.
• Create a controller at the bottom of your bone D.
• Parent this bone to the foot controller.
• Parent the pole target of your calf to the foot controller.
• Add a Copy Location constraint to your foot so that it sticks to the calf.
• Add a Damped Track or an IK constraint to the bone D and choose the new controller as your Target

Also note that you can limit the IK bones rotations in Properties > Bone > Inverse Kinematics, or with a Limit Rotation constraint, depending on the bones and the chosen solution.

So, here is the solution we've found:

• Create a controller for your foot, deparent it, parent the foot to this controller.
• Choose this controller as the Target of your calf's IK.
• The Chain Length of your calf's IK constraint must be 2.
• Create a new controller at the bottom of your bone D.
• Parent this second controller to the foot controller (Keep Offset).
• Parent the pole target of your calf to the foot controller (Keep Offset).
• Add a Copy Location constraint to your foot so that it sticks to the calf.
• Add a Damped Track or an IK constraint to the bone D and choose the new controller as your Target

Also note that you can limit the IK bones rotations in Properties > Bone > Inverse Kinematics, or with a Limit Rotation constraint, depending on the bones and the chosen solution.

So, here is the solution we've found:

• The Chain Length of your calf's IK constraint must be 2.
• Create a controller on the bottom of your bone D.
• Parent this bone to the foot controller.
• Parent the pole target of your calf to the foot controller.
• Add a Copy Location constraint to your foot so that it sticks to the calf.
• Add a Damped Track or an IK constraint to the bone D and choose the new controller as your Target

So, here is the solution we've found:

• The Chain Length of your calf's IK constraint must be 2.
• Create a controller at the bottom of your bone D.
• Parent this bone to the foot controller.
• Parent the pole target of your calf to the foot controller.
• Add a Copy Location constraint to your foot so that it sticks to the calf.
• Add a Damped Track or an IK constraint to the bone D and choose the new controller as your Target

Also note that you can limit the IK bones rotations in Properties > Bone > Inverse Kinematics, or with a Limit Rotation constraint, depending on the bones and the chosen solution.

If you assign a IK constraint to the bone D, with a controller on its bottom, perhaps with no pole target, but just a target controller, and assign a Child Of to this controller with the first controller as the Target (click on Set Inverse)? Also note that you can limit the IK bones rotations in Properties > Bone > Inverse Kinematics, so it doesn't go crazy

So, here is the solution we've found:

• The Chain Length of your calf's IK constraint must be 2.
• Create a controller on the bottom of your bone D.
• Parent this bone to the foot controller.
• Parent the pole target of your calf to the foot controller.
• Add a Copy Location constraint to your foot so that it sticks to the calf.
• Add a Damped Track or an IK constraint to the bone D and choose the new controller as your Target