Thank you for the additional information. Now I understand what the problem is. I will presume that as written, the present court order grants the mother physical custody at this time and she is now attempting to enforce that right.
Police generally will not get involved in custody disputes like this, and so it is unlikely that she will appear at the house with the police.
However, you might consider filing a Petition for Emergency Custody today and hope that a judge agrees to grant you sole Managing Conservatorship until a hearing can be had on a modification of the custody order.
This is something that must be handled quickly, or you may find the mother filing against you for Contempt. the fact that the mother has acted like a nut case in the recent passed and asked you to keep the child does not give you the right to refuse her custody if the court order is still in place. You need the court to resolve this issue as soon as possible.
Speak to a local Family Law
attorney today about taking care of this. It will be much better in the long run for your child. Also, based on the age of your child, the court will consider which parent they want to live with as well---Texas child custody law states that children 12 years of age or older can contribute to the custody decision-making process----so do make the motion for modification of custody as soon as possible.
I hope that you found my answer informative, that you are accepting of my efforts and that you will rate my efforts based on the knowledge I have provided to you.
I wish you the best in 2012.