How to add jQuery script to a custom visual webpart?

Similar to some previous questions, I'm trying to use jQuery in a visual web part but I keep getting that jQuery is undefined. I've added the jQuery script to SiteAssets as well as a script folder inside my visual webpart project, and tried referencing it in the ascx file with both:

<script src="~sitecollection/SiteAssets/jquery-1.9.1.min.js"></script>
<script src="./Scripts/jquery-1.9.1.min.js"></script>

And also in code behind, in the Page_Load method, with lines such as:

this.Page.ClientScript.RegisterClientScriptInclude(this.GetType(), "custJquery1", "~/SiteAssets/jquery-1.9.1.min.js");
this.Page.ClientScript.RegisterClientScriptInclude(this.GetType(), "custJquery2", "~sitecollection/SiteAssets/jquery-1.9.1.min.js");
this.Page.ClientScript.RegisterClientScriptInclude(this.GetType(), "custJquery2", "/SiteAssets/jquery-1.9.1.min.js");

I've also tried not referencing jQuery anywhere because I thought maybe the page (Discussion board topics) I'm using the webpart may already have jQuery on it.

The javascript I am using to check the jquery in my ascx file is:

<script type="text/javascript">
    function TheFunctionToDoTheWork() {
        if (typeof jQuery == 'undefined') {
            alert('jQuery didnt load');
        }
        else
            alert("Ive never received this message");
    }

    // "Subscribe to the SharePoint "page load"
    _spBodyOnLoadFunctionNames.push('TheFunctionToDoTheWork');
</script>

All I ever get is the alert that 'jQuery didnt load'. What might be wrong?