How do I delete _object properly?

PolymorphismProblem.cpp

class SomeClass
{
private:
    int someMember;
};

class Base
{
public:
    Base()
    {
        _member = new SomeClass();
    }
    virtual ~Base()
    {
        delete _member;
    }
protected:
    SomeClass *_member;
};

class ExtendA public Base
{
public:
    ExtendA() : Base()
    {
        _memberA = new SomeClass();
    }
    virtual ~ExtendA()
    {
        delete _memberA;
    }
private:
    SomeClass *_memberA;
};

class ExtendB public Base
{
public:
    ExtendB() : Base()
    {
        _memberB = new SomeClass();
    }
    virtual ~ExtendB()
    {
        delete _memberB;
    }
private:
    SomeClass *_memberB;
};

class Controller
{
public:
    Controller()
    {
        _object = 0;
    }
    Base *object() const
    {
        return _object;
    }
    void setObject(Base *o)
    {
        if (_object)
            delete _object;     // <====== PROBLEM
        _object = o;
    }
    
private:
    Base *_object;
};